Cleanup: disable debug print define in override code.

Thanks to Blazej Floch (@bfloch) for the head-up.

Fix stupid misplacement of depsgraphs extraction/restoration.

Merge branch 'undo-experiments' into undo-experiments-swap-reread-datablocks

Merge branch 'undo-experiments' into undo-experiments-remap-history

Merge branch 'master' into undo-experiments

Fix T71596: Bug in io_utils api breaking only on windows.

Stupid mistake, 'original' filepath is a blender-flavored one, with
potentially weird things like the '//' relative 'header'... This can
work on linux (also it could have broken in other places too), but on
windows that is fully invalid path and python `os.path` library just
generates empty result here.

Simply using proper valid path instead fixes it...

Undo: initial attempt to use ID swap to address pointers remapping issue.

Not really working right now...

Undo: Initial wip useless to handle ID pointers issues through more mappings.

Don't think this is a working solution in fact, for at least two
reasons:
* Chaining Undo and Redo steps in random paterns with some ID being
reused and others being new all the time would require a very complex
system to keep track of all those changes and keep being able to remap
properly pointers from unread datablocks the the right new memory of
read datablocks.
* As small as it is, there is a risk of pointer collision here, and I
cannot see how to 100% handle it safely and sanely.

Undo: Re-use existing IDs from old bmain: do not search by name.

This is actually a fairly bad idea, since IDs can be renamed...

Only search by pointer value now, this *should* work in all expected
cases once undo/redo fully reuses unchanged data-blocks.

Undo: save/restore DEG closer to the actual undostep.