Improve inference by not considering thisless functions to be context-sensitive

#62243

• People have tried to implement this incorrectly in the past
• This one seems good though
• There was some discussion about const type parameters, not quite sure how that's related?
  • Someone just mentioned it as a workaround for the issue
• Agree we want this
• Extended test suites highlight only a couple issues - already analyzed in PR body, nothing concerning

Program diagnostics change in Corsa

• Type reference directive error appears in both Strada and Corsa, but is not silenceable with --skipLibCheck in Corsa
• May just need to filter diagnostics where they're produced?
• Really just checking whether this is a bug or an intended behavior change
• It's a bug
• Is this a change to invalidation constraints around changing --skipLibCheck?
  • No