Step#1 MDEV-27896 Wrong result upon `COLLATE latin1_bin CHARACTER SET latin1`...

Step#1 MDEV-27896 Wrong result upon `COLLATE latin1_bin CHARACTER SET latin1` on the table or the database level

- Adding data type aliases:
  using Lex_column_charset_collation_attrs_st = Lex_charset_collation_st;
  using Lex_column_charset_collation_attrs = Lex_charset_collation;

  and using them all around the code (except lex_charset.*)
  instead of the original names.

- Renaming Lex_field_type_st::lex_charset_collation()
  to charset_collation_attrs()

- Renaming Column_definition::set_lex_charset_collation()
  to set_charset_collation_attrs()

- Renaming Column_definition::lex_charset_collation()
  to charset_collation_attrs()

Rationale:

The name "Lex_charset_collation" was a not very good name.
It does not tell details about its properties:
1. if the charset is optional (yes)
2. if the collation is optional (yes)
3. if the charset can be exact (yes) or context (no)
4. if the collation can be: exact (yes) or context (yes)
5. if the clauses can be repeated multiple times (yes)

We'll need a few new data types soon with different properties.
For example, to fix MDEV-27896 and MDEV-27782, we'll need a new
data type which is very like Lex_charset_collation, but additionally
supports CHARACTER SET DEFAULT (which is allowed on table and database level,
but is not allowed on the column level yet), i.e. with:
  "the charset can be exact (yes) or context (yes)" in N3.

So we'll have to rename Lex_charset_collation to something else,
e.g.: Lex_exact_charset_extended_collation_attrs,
and add a new data type:
e.g. Lex_extended_charset_extended_collation_attrs

Also, we'll possibly allow CHARACTER SET DEFAULT at the column level for
consistency with other places. So the storge on the column level can change:
- from Lex_exact_charset_extended_collation_attrs
- to   Lex_extended_charset_extended_collation_attrs

Adding the aliases introduces a convenient abstraction against
upcoming renames and c++ data type changes.

sql/field.h

@@ -5501,7 +5501,8 @@ class Column_definition: public Sql_alloc,
 
   bool check_vcol_for_key(THD *thd) const;
 
-  void set_lex_charset_collation(const Lex_charset_collation_st &lc)
+  void set_charset_collation_attrs(const
+                                   Lex_column_charset_collation_attrs_st &lc)
   {
     charset= lc.charset_collation();
     if (lc.is_contextually_typed_collation())
@@ -5509,7 +5510,7 @@ class Column_definition: public Sql_alloc,
     else
       flags&= ~CONTEXT_COLLATION_FLAG;
   }
-  Lex_charset_collation lex_charset_collation() const
+  Lex_column_charset_collation_attrs charset_collation_attrs() const
   {
     return Lex_charset_collation(
              charset,

sql/item_func.h

@@ -3773,7 +3773,7 @@ struct Lex_cast_type_st: public Lex_length_and_dec_st
   }
   bool set(const Type_handler *handler,
            const Lex_length_and_dec_st & length_and_dec,
-           const Lex_charset_collation_st &cscl,
+           const Lex_column_charset_collation_attrs_st &cscl,
            CHARSET_INFO *defcs)
   {
     CHARSET_INFO *tmp= cscl.resolved_to_character_set(defcs);

sql/json_table.cc

@@ -874,7 +874,7 @@ int Json_table_column::set(THD *thd, enum_type ctype, const LEX_CSTRING &path,
 
 
 int Json_table_column::set(THD *thd, enum_type ctype, const LEX_CSTRING &path,
-                           const Lex_charset_collation_st &cl)
+                           const Lex_column_charset_collation_attrs_st &cl)
 {
   if (cl.is_empty() || cl.is_contextually_typed_collate_default())
     return set(thd, ctype, path, nullptr);

sql/json_table.h

@@ -161,7 +161,7 @@ class Json_table_column : public Sql_alloc
   }
   int set(THD *thd, enum_type ctype, const LEX_CSTRING &path, CHARSET_INFO *cs);
   int set(THD *thd, enum_type ctype, const LEX_CSTRING &path,
-          const Lex_charset_collation_st &cl);
+          const Lex_column_charset_collation_attrs_st &cl);
   Json_table_column(Create_field *f, Json_table_nested_path *nest) :
     m_field(f), m_nest(nest), m_explicit_cs(NULL)
   {

sql/lex_charset.h

@@ -196,4 +196,8 @@ class Lex_charset_collation: public Lex_charset_collation_st
 };
 
 
+using Lex_column_charset_collation_attrs_st = Lex_charset_collation_st;
+using Lex_column_charset_collation_attrs = Lex_charset_collation;
+
+
 #endif // LEX_CHARSET_INCLUDED

sql/sql_table.cc

@@ -2202,7 +2202,7 @@ bool check_duplicates_in_interval(const char *set_or_name,
 bool Column_definition::
        prepare_charset_for_string(const Column_derived_attributes *dattr)
 {
-  CHARSET_INFO *tmp= lex_charset_collation().
+  CHARSET_INFO *tmp= charset_collation_attrs().
                        resolved_to_character_set(dattr->charset());
   if (!tmp)
     return true;

sql/sql_type.cc

@@ -2715,7 +2715,7 @@ Type_handler::Column_definition_set_attributes(THD *thd,
                                                column_definition_type_t type)
                                                const
 {
-  def->set_lex_charset_collation(attr.lex_charset_collation());
+  def->set_charset_collation_attrs(attr.charset_collation_attrs());
   def->set_length_and_dec(attr);
   return false;
 }

sql/sql_yacc.yy

@@ -5789,10 +5789,10 @@ field_type_or_serial:
           }
           field_def
           {
-            Lex_charset_collation tmp= $1.lex_charset_collation();
+            Lex_charset_collation tmp= $1.charset_collation_attrs();
             if (tmp.merge_charset_clause_and_collate_clause($3))
               MYSQL_YYABORT;
-            Lex->last_field->set_lex_charset_collation(tmp);
+            Lex->last_field->set_charset_collation_attrs(tmp);
           }
         | SERIAL_SYM
           {
@@ -11358,7 +11358,7 @@ json_table_column_type:
                                             COLUMN_DEFINITION_TABLE_FIELD);
             if (Lex->json_table->m_cur_json_table_column->
                   set(thd, Json_table_column::PATH, $3,
-                      $1.lex_charset_collation()))
+                      $1.charset_collation_attrs()))
             {
               MYSQL_YYABORT;
             }
@@ -11369,7 +11369,7 @@ json_table_column_type:
                                             COLUMN_DEFINITION_TABLE_FIELD);
             if (Lex->json_table->m_cur_json_table_column->
                   set(thd, Json_table_column::EXISTS_PATH, $4,
-                      $1.lex_charset_collation()))
+                      $1.charset_collation_attrs()))
                MYSQL_YYABORT;
           }
         ;

sql/structs.h

@@ -699,14 +699,15 @@ struct Lex_field_type_st: public Lex_length_and_dec_st
   }
   void set(const Type_handler *handler,
            const Lex_length_and_dec_st &length_and_dec,
-           const Lex_charset_collation_st &coll)
+           const Lex_column_charset_collation_attrs_st &coll)
   {
     m_handler= handler;
     m_ci= coll.charset_collation();
     Lex_length_and_dec_st::operator=(length_and_dec);
     m_collation_type= ((uint8) coll.type()) & 0x3;
   }
-  void set(const Type_handler *handler, const Lex_charset_collation_st &coll)
+  void set(const Type_handler *handler,
+           const Lex_column_charset_collation_attrs_st &coll)
   {
     m_handler= handler;
     m_ci= coll.charset_collation();
@@ -734,10 +735,10 @@ struct Lex_field_type_st: public Lex_length_and_dec_st
   }
   const Type_handler *type_handler() const { return m_handler; }
   CHARSET_INFO *charset_collation() const { return m_ci; }
-  Lex_charset_collation lex_charset_collation() const
+  Lex_column_charset_collation_attrs charset_collation_attrs() const
   {
-    return Lex_charset_collation(m_ci,
-                                 (Lex_charset_collation_st::Type)
+    return Lex_column_charset_collation_attrs(m_ci,
+                                 (Lex_column_charset_collation_attrs_st::Type)
                                  m_collation_type);
   }
 };
@@ -768,7 +769,7 @@ struct Lex_dyncol_type_st: public Lex_length_and_dec_st
     m_ci= cs;
     Lex_length_and_dec_st::reset();
   }
-  bool set(int type, const Lex_charset_collation_st &collation,
+  bool set(int type, const Lex_column_charset_collation_attrs_st &collation,
            CHARSET_INFO *charset)
   {
     CHARSET_INFO *tmp= collation.resolved_to_character_set(charset);