Add tips detection to auto mapping in bone mapper

[TokageItLab]

Fixes #89725.

GodotHumanoid does not have a metacarpal for fingers other than the thumb. To avoid assigning them incorrectly, it is necessary to assign from the ends. However, some models might have "Tips" or "Leaf" bones to provide length information, so assigning from the ends is problematic.

This PR, make auto mapping can detected Tips and the mapping will be offset when candidate bones for the fingers has the name Tip or Leaf, or if none of the meshes have weights bound to them.

If the joint count of fingers excluding the thumb is the same, if even one Tip is detected, it will be apply by all bones. This is because the ReadyPlayerMe model is weird since only the index finger tips has weight.

This becomes a problem in cases where you intentionally have tips on only one finger, so if the number of bones is different, determine the tips individually. Still it may be a problem if the number of fingers is the same and you forget to bind only a specific finger, but I consider it is a rare case.

Make the detection based on the name match and the number of children in the thumb method by @lyuma.

[lyuma]

Added some more test files which do not contain any mesh.

I am skeptical of using mesh vertex-based approaches, since files such as these do not contain any mesh at all:
simple_vrm_rig.glb.gz - This one is in T-pose
simple_vrm_rig_anim4.blend
simple_vrm_rig_nlaonly2.fbx - this is animated and not in t-pose

I'll test the PR and see if I can offer any changes.
For example, I ran into a similar problem in Unidot (which uses a copy of Godot's skeleton profile guesser) and I came up with this approach:
V-Sekai/unidot_importer@4f4f62c
However, I am a little concerned that this does not sufficiently address cases where there are two _End bones (which happens when importing and re-exporting an animation FBX with the default setting of "Add Leaf Bone"
But maybe it will mitigate the most common cases

[TokageItLab]

Indeed it is little skeptical, but since BoneMap is reusable, so I think this implementation would be a not big problem. So it would work as a workaround to use a BoneMap generated for a model with a mesh in an animation file without a mesh, as long as they have the same bone name.

[TokageItLab]

From discussed with @lyuma, we think we can add a couple of decision points, so I will add them.

So the steps with the following priority order should be used for estimation:

1. put "distal" in the search suggestions
2. if the number of thumb bones is 4, there are Tips
3. look at the mesh weights

[TokageItLab]

Detection by the number of thumb children conflicts with detection from weights. Probably, given the existence of skeletons without skins, detection by the number of thumb children should be preferred. Therefore, I will adopt @lyuma's method overall, thanks.

[lyuma]

Reviewed on a call with fire. I think this is good. It can use more testing, but that's what beta is for.

What's important is this improves Mixamo and ReadyPlayerMe compatibility by adding a few heuristics, so I think it's fairly safe.

[akien-mga]

Thanks!