Move MovieClip to new undo cache management system.

Fix utterly broken code regarding GPUtextures of MovieClip in readfile.c

Treat those as pure runtime code, reset to NULL by reading code, for
now.

Think those could be handled like Image gputextures (i.e. considered
runtime cache and preserved across undo steps), but probably not
critical for now.

Move Scene's cache management during undo to new system.

Move volume to new cache management system for undo.

Add key structure and hashing utils for ID caches.

Part of D8183, refactoring how we preserve caches across undo steps in
readfile code.

IDTypeInfo: add new callback to loop over all cache pointers of an ID.

Part of D8183, refactoring how we preserve caches across undo steps in
readfile code.

Readfile/Undo: initial refactor of cache preservation code.

Main goal here is to have better specificity using cache keys, to avoid
same memroy address being re-used messing up with cache pointers
restoration after undo had to re-read a data-block.

Once all caches handling are ported to this new system, it should fix
random issues like the one reported in T76989.

Part of D8183, refactoring how we preserve caches across undo steps in
readfile code.

New undo cache management: Add Image IDs.

Some notes:
* `Image.cache` acts as some kind of 'main' cache, when it is NULL
(could not be restored), other caches should also be cleared. Oddly
enough, previous code was not clearing **all** caches, could not find
any reason for that behavior, so new code does a full clear.
* `imamap` is still used for Node previews from scenes' compositor,
however this is actually fully disabled in `direct_link_node()`.
* For render slots we cannot use offsetof as third part of the cache
key, so we are using a hash of the slot's name instead.

As far as I can tell, this fixes T76989: Visual glitches when undo after
reload multiple images by script (in Material Preview).

Cleanup: do not use magic values for enums...

Move bSound cache handling during undo to new system.