gh-141939: Add colors to interpolated values in argparse

[alexprengere]

• Issue: Add colours to argparse interpolated values in --help #141939

[mpkocher]

Consider adding a test or extending an existing test.

[alexprengere]

Of course 😉 (this is a draft PR).
I will extend the color test in test_argparse, I wanted to be sure whether to color all interpolated values or just default.
Also I am unsure whether to re-use theme.default_value or introduce new values in _colorize.py like #141680 did.
I will clean this up tomorrow and then mark it as ready for review.

[alexprengere]

I updated the code and tests 😉

I had to change a bit the logic introduced in #141680 as introducing a new color for interpolated values, that would be different from the default_value color, is a bit complex to handle.

For ArgumentDefaultsHelpFormatter, as _get_help_string returns the %(default)s already "colored", updating _expand_help to "color" interpolated values would essentially color the default values twice, and no longer respect the default_value color.
So I removed the coloring of %(default)s in _get_help_string, and now it happens in _expand_help, as the default value will be colored, along all interpolated values, using a sinple interpolated_value color.

I hope this is clear, I can amend this if needed.

[alexprengere]

For the record the PR could be slightly improved with the formatting of choices, by coloring each individual values before joining them with ', '.
I tried it but encountered bug in an unrelated part (filed in #142035):

The issue is that the use of textwrap.wrap happens after the ANSI codes have been inserted, causing the wrapping to be broken in some cases.