Blender imports will always start within `.godot/imported` folder because we first convert the .blend file to .gltf, store it in `.godot/imported` and run the import from there, so on-disk resources linked from .blend files end up with duplicate textures.
This helps, for importers spitting out new resources to the res://
filesystem to actually hash them to generate deterministic UIDs.
This PR also fixes the determinism for translations.
Individual bones are not represented as `Node`s in Godot, in order to support meta functionality for them the skeleton has to carry the information similarly to how other per-bone properties are handled.
- Also adds support for GLTF import/export
This is useful for custom tagging of objects with properties (for example in Blender) and having this available in the editor for scripting.
- Adds import logic to propagate the parsed GLTF extras all the way to the resulting Node->meta
- Adds export logic to save Godot Object meta into GLTF extras
- Supports `nodes`, `meshes` and `materials` (in GLTF sense of the words)
