Reformat "Important Files" section in compiler.rst

[ezio-melotti]

This is a follow-up of #984 that reformats the "Important Files" section in compiler.rst:

I also found another issue with this section: https://devguide.python.org/internals/compiler/#important-files
In addition to the fact that the listed files don't use any markup, the markup used for most of the files seem incorrect (it's a blockquote due to the indentation). A nested list with full paths for all the files and :cpy-file: should be a better alternative.

In the PR I added links to the files using :cpy-file: and reformatted the list.

Before:

After:

[hugovk]

Couple more deleted files, the rest look okay.

Otherwise looks good, thanks!

[ezio-melotti]

The deleted files are tracked in #1003.

[CAM-Gerlach]

If we're reformatting the whole section like this, maybe worth fixing the lexicographic order too while we're at it?

[ezio-melotti]

I think they are roughly sorted from most to least important.

[CAM-Gerlach]

LGTM then, thanks @ezio-melotti