Blender 3.0 will only support single-frame Actions in the pose library.
The goal of this patch is to lay the groundwork for making it possible
for the Asset Browser to reject/hide "animation snippet" Action assets.
Determining whether an Action has one or more frames (i.e. whether it
has a single pose or animation) requires inspecting the Action itself,
and thus loading the data-block itself. This would make it impossible to
quickly determine from the asset browser.
To solve this, the Action is inspected before saving, and a
`"is_single_frame"` boolean (well, 0/1 integer) IDProperty is added.
Reviewed by: Severin
Differential Revision: https://developer.blender.org/D13202
Correctly reset `prev` and `next` pointers of action group FCurves when
separating them into distinct `ListBase`s per `bActionGroup`.
These `NULL` pointers are necessary to temporarily demarcate the start &
end of the `bActionGroup::channels` list. Having them still point to
other FCurves caused ordering issues when moving curves towards the
start/end of a group.
This commit corrects the above issue and adds versioning code to rectify
any ordering issues that may have been caused. For this purpose the
`BKE_action_groups_reconstruct()` function is rewritten to avoid relying
on the `bAction::curves` list order or `prev` link integrity.
Differential Revision: https://developer.blender.org/D11811
