affected by a tk regression.  Initial patch by Mark Roseman.

now work on Mac Aqua.  Patch by Mark Roseman.

Start to split regrtest.py into smaller parts with the creation of
Lib/test/libregrtest/cmdline.py: code to handle the command line, especially
parsing command line arguments. This part of the code is tested by
test_regrtest.

make opening brace of container literals and comprehensions correspond to the line number and col offset of the AST node (closes #25131)

This associates the message box with the widget and is better for Mac OSX.
Patch by Mark Roseman.

Some of the calls to the Frm class were buggy anyway.

The height is reduced by 3/4 to account for extra spacing between lines,
relative to an Idle editor, and extra tall header lines.

by adding a new tag.  Patch by Mark Roseman. Also give <pre> text a very
light blueish-gray background similar to that used by Sphinx html.

* Change limit type from unsigned int to Py_UCS4, to use the same type than the
  "ch" variable (an Unicode character).
* Reuse ch variable for _Py_ERROR_XMLCHARREFREPLACE
* Add some newlines for readability

Fixed error creation if the problem is an empty expression in an f-string: use ast_error instead of PyErr_SetString.