Matt Johnson

Rebased on the current dev branch to pick up the fixes from #2733 / 6575a265a73de63a50559b22626ee723e3ba2059.

> Thanks, @mattyjams ! We are actually IP on adding new elementTypes `point` and `edge` for use initially in UsdPhysics, so in your checks relating to `materialBind` family, it would...

Rebased to resolve merge conflicts.

Rebased and resolved merge conflicts.

Freshening with a rebase on the current dev branch (35dbce15eb3dc6c805b65135d911c246716fd192).

I caught up with @tallytalwar about this and I'm going to take a crack at re-formulating this in terms of the new `UsdValidator` framework in C++ instead.

Closing this in favor of #3123, which implements the same checks but in the new C++ validation framework...

Freshening this with a rebase on the current dev branch, but I also added a commit for the `Ts` library where it looks like instances of `std::shared_ptr::unique()` crept in when...

Freshening with a rebase on the current dev branch (35dbce15eb3dc6c805b65135d911c246716fd192).

Rebased on the current dev branch (5332d627cb28991e812acd67b8971e87367d9191) and resolved conflicts in `stb_image.patch` from the merge of #2880.