Bisect improvements

[andrewbranch]

Change described microsoft/TypeScript#50670 (comment):

The issue with the bisect was that the culprit commit was cherry-picked from main to release-4.5, and I only look at the timeline of commits going into main. I’m far from a git expert, but (warning: likely butchering terminology ahead) git bisect gets mad if you give it a pair like v4.4.4 and v4.5.5 because those tags exist on separate branches off of main that never reunite with main. To account for that, I actually run the bisect between the merge-base of the respective inputs and main, so I’m actually bisecting between the point where release-4.4 and release-4.5 branched off of main. But in hindsight I think I only need to take the merge-base of the old ref. There still might be a problem if the behavior is different between the old ref and its merge base with main, though. I think that should be less common.

This also changes the GH Action API a bit; TypeScript PR incoming.

[jakebailey]

I do bisects between tags on different branches all time time when bisecting by hand; it just starts by testing the merge base first automatically and bails out if that commit doesn't have the "old"/"good" behavior. (Maybe I'm confused and that's what you're reimplementing in TS?)

[andrewbranch]

Hm, I had some kind of trouble with it when I was first setting this up. Don’t recall exactly how.