ENH: Handle the value attribute in F2Py wrappers

[HaoZeke]

Closes #21665. The implementation essentially takes advantage of the existing machinery which is very similar to the handling of intent(c).

This should cover everything which is allowed by the standard since:

Character values, substrings, assumed-size arrays, and adjustable arrays cannot be passed by value. [source]

Might need a release note, but then again maybe not.

[melissawm]

Looks good to me - should probably be documented somewhere, +1 to add a release note. Thanks @HaoZeke !

[charris]

Needs a release note.

[melissawm]

Thanks @HaoZeke !