Maya native usd plugin

Also a quick Blender test:

Had to do this in a temporary branch to merge both the USD branch with the draft for the New Publisher in Blender - anyway, that test branch is here: enhancement/blender_usd


The feature request in the post has been added by this PR.
Many many thanks to @BigRoy :heart:

Just wanted to add to this that using variants for LODs isn’t necessarily the best USD use case of variants because Variant selections can’t be animated over time and as such, if an objects moves closer or further away you can’t technically animate the LOD unless say you’d write a USD file per frame and render that instead.