Implement naming version system for FBX and Blend importers like glTF

[aaronfranke]

Based on the request here #106537 (comment)

This is the same as the system introduced in PR #84271 and is important for preserving compatibility due to changes introduced in PR #104184, PR #106537, and PR #80270.

This PR implements the same naming version system found in glTF in the UFBX, FBX2glTF, and Blend editor scene format importers, with UFBX getting a new _naming_version field, and FBX2glTF/Blend forwarding this to GLTFDocument.

This should make FBX and Blender files imported in Godot <= 4.4 behave the same in Godot 4.5 and later, because they will automatically have this naming version set for compatibility. This only applies to files imported in older Godot versions with existing .import files. Any brand new files without .import files will be given the latest version.

In FBXDocument, I am using the same naming version numbers as glTF. There is no behavior difference between version 0 (Godot 4.0 and 4.1) and version 1 (Godot 4.2 to 4.4). For version 2, there is one difference in a call to SkinTool introduced by PR #104184, which will collapse non-joint leaf bones with version 0 or 1, and not collapse them in version 2 or later. There will also be a difference with PR #106537 when it is updated to use this option.

For both UFBX and FBX2glTF, we are forced to pick just one name for both, so I went with fbx/naming_version, even though FBX2glTF's one is better described as gltf/naming_version. It doesn't really matter, though.

[lyuma]

Merge this after #106537

Once that is merged, change the last argument of _create_skeletons in fbx_document.cpp line 2228 to pass _naming_version instead of 2

[akien-mga]

Thanks!