To review: PRs requiring Vinita approval

[BenHenning]

The following PRs require post-merging PR approval from @vinitamurthi (@BenHenning):

• Fix part of #4044: Add protos & testing library for commutative expressions/operations #4049
• Fix #3622, #4238, #3861, part of #4044: Fix state player deadlock by migrating progress controllers over to a command-queue structure #4239
• Fix #4044: Introduce UI support for math expressions & new interactions #2173

Note that these were force-merged due to the sensitive timeline they're part of.

Reviewer: please review the above PRs & check them off once complete. Assign back to me once all have been addressed. Comments can be left directly on the original PRs, and I'll follow up with one PR to address all of them (if code changes are needed, otherwise I'll follow up on the corresponding PRs). This issue should only be closed once you're satisfied with all of the changes, including needed follow-up changes.

[BenHenning]

Since I authored these PRs and now have @vinitamurthi's codeowners, I'm considering this done by virtue of me self-reviewing my code as I go along (and because I can't approve my own PRs).