Add assert comments in CodeFixes and Refactors

[RyanCavanaugh]

Our telemetry-sourced bugs have a ton of call stacks like this, where it isn't obvious which refactor triggered it (tons of them have a doChange function) and it isn't obvious which assert failed without checking out very specific versions of tsserver.js and digging into the line numbers:

Error: Debug Failure. False expression.
    at doChange (tsserver.js:116689:22)
    at unknown (tsserver.js:116680:96)
    at Function.ChangeTracker.with (tsserver.js:111861:17)
    at Object.getCodeActions (tsserver.js:116680:64)
    at unknown (tsserver.js:112847:121)
    at Object.flatMap (tsserver.js:573:25)
    at Object.getFixes (tsserver.js:112847:23)
    at unknown (tsserver.js:122423:35)
    at Object.flatMap (tsserver.js:573:25)
    at Object.getCodeFixesAtPosition (tsserver.js:122421:23)
    at suppressed_frame()
    at suppressed_frame()
    at IOSession.Session.getCodeFixes (tsserver.js:131477:64)

This PR adds messages to all the assert* family calls in these two folders. As a follow-up we could also do the same for cast as that has a few ambiguous stacks as well.

In most cases I tried to make the assert messages globally unique rather than making them consistent, since this will make looking them up later easier.