Accept line_code and position when importing

app/models/concerns/diff_positionable_note.rb

@@ -5,7 +5,7 @@ module DiffPositionableNote
   included do
     delegate :on_text?, :on_image?, to: :position, allow_nil: true
     before_validation :set_original_position, on: :create
-    before_validation :update_position, on: :create, if: :on_text?
+    before_validation :update_position, on: :create, if: :on_text?, unless: :importing?
 
     serialize :original_position, Gitlab::Diff::Position # rubocop:disable Cop/ActiveRecordSerialize
     serialize :position, Gitlab::Diff::Position # rubocop:disable Cop/ActiveRecordSerialize

app/models/diff_note.rb

@@ -21,7 +21,7 @@ class DiffNote < Note
   validate :positions_complete
   validate :verify_supported
 
-  before_validation :set_line_code, if: :on_text?
+  before_validation :set_line_code, if: :on_text?, unless: :importing?
   after_save :keep_around_commits, unless: :importing?
   after_commit :create_diff_file, on: :create
 
@@ -104,7 +104,7 @@ class DiffNote < Note
   end
 
   def should_create_diff_file?
-    false && on_text? && note_diff_file.nil? && start_of_discussion?
+    on_text? && note_diff_file.nil? && start_of_discussion?
   end
 
   def fetch_diff_file