bug#44297: [Feature request] project.el: Additional utility functions

[Juri Linkov <juri@linkov.net>]

> I think the term is pretty much established:
> https://www.emacswiki.org/emacs/FindOtherFile
>
> Projectile also has a command with a similar name.

Then the name 'other-file' is fine.

> The feature will be pretty C/C++-centric, but I suppose it's useful enough.

It's also useful with Web development: while VueJS can keep parts of
components in one file .vue, other frameworks require 3 different files:
file.html, file.js and file.css.

>> Another useful command would be:
>> project-find-file-only using completing-read to match on file names only,
>> not on directory parts.
>
> And then... disambiguate files with the same base name with another prompt?
>
> IME, having multiple files with the same name in the project is very
> common. Your experience can vary, though.
>
> A fuzzy search across full names works best for me, personally. We could
> also try some differently weighted, fuzzy matching styles.

I don't know if the required completion can be part of a fuzzy search,
but it should show exactly the same completions as the current command
(with directory and file names), but should match only on file name parts,
not on directory name parts, e.g. with files:

  dirname/filename1 dirname/file2

typing "name" for completions should show only "dirname/filename1",
because most of the time, project directory names get in the way
when searching for a file by its name, and part of file name matches
directory names with many other unrelated files.

>>> project-recentf: completing-read recently-accessed files in the project
>> All project file-reading commands could provide a list of recent files
>> as the default values available via M-n key presses.
>
> Perhaps a flat, immediately visible list will have its own value, though?

Sorted by recency?