Depends on D20988. Ref T13395. Ref T13098. Ref T13203.

This brings all the "toolsets" code into "master". We try to run commands as toolsets commands first, then fall back to older code.

Since the "toolsets" class tree is mostly parallel to the older class tree, this isn't completely broken. Currently, all commands fall back.

Created this diff, ran various other commands. But this is probably a long shot from finished.