This setting is set to _off_ on some imported animation files;
in this case, tangent data is not used and the curve is interpolated linearly.
Previously, we would sometimes set this to on as part of various animation
manipulations we perform in MA processing; this broke some avatars, e.g. "Fluria".
The previous logic failed when duplicate PBs explicitly specify their root transform.
This change rewrites this logic and expands the cases in which PBs are pruned.
This branch rewrites the merge armature logic to be both simpler and more reliable. In particular, all components in the merged armature will always be moved into the target armature, eliminating the need for complex and unreliable constraint adjustments. I also rewrite the path remapping logic to be more reliable by tracking actual GameObjects, rather than string paths.
This change fixes a number of constraint-heavy outfits, including:
* https://cloudz.booth.pm/items/3751948
* https://capettiya.booth.pm/items/4424678
It also fixes issues with some more advanced use cases, such as animating transforms on bones that are newly added using merge armature.
