Adds a bool import option `nodes/import_as_skeleton_bones`.
This is supported in all FBX or GLTF document based formats.
It is especially useful for retargeting and importing animations.
This allows Godot to automatically compress meshes to save a lot of bandwidth.
In general, this requires no interaction from the user and should result in
no noticable quality loss.
This scheme is not backwards compatible, so we have provided an upgrade
mechanism, and a mesh versioning mechanism.
Existing meshes can still be used as a result, but users can get a
performance boost by reimporting assets.
Tooltips are displayed when hovering import options, both in the Import
dock and in the import defaults editor (which is in the Project Settings).
Co-authored-by: Rémi Verschelde <rverschelde@gmail.com>
