.blend scene importer lacks documentation

**Your Godot version:**
4.5 dev5

**Issue description:**
The .blend scene importer is almost entirely undocumented. The only thing I can find is listed below, which doesn't say anything about the settings of the importer, only how to set it up and how it works.

The importer also has no doc comments on any of the properties. This lack of documentation makes it hard to use and report issues to improve it, because I can't know if something isn't working right if I can't know how it's _supposed_ to work.

**URL to the documentation page (if already existing):**
This is all the documentation I can find: https://docs.godotengine.org/en/stable/tutorials/assets_pipeline/importing_3d_scenes/available_formats.html#importing-blend-files-directly-within-godot