bug#58253: Add a command to show a diff before `M-x recover-this-file'

[Stefan Kangas]

Severity: wishlist

After a crash with a file with unsaved changes, Emacs says:

    <foo> has auto save data; consider M-x recover-this-file

My usual response if I care enough about the file, and it is not under
version control, is to manually make a copy of it, run M-x
recover-this-file, save the resulting file, and then check the diff
between the resulting file and the copy.

It would be useful with a command to show the diff directly from Emacs.

This was previously discussed in:
https://lists.gnu.org/r/emacs-devel/2022-10/msg00065.html