Make bash window prompt adjuster more strict

[Tyriar]

Fixes #210773

@cpendery since you use git bash this might impact you. Are prompts in git bash apart from a simple $ common?

[cpendery]

@Tyriar, the $ is the default, but I have seen people customize them. I've been experimenting with sending over the prompt terminator, similar to how I sent the prompt height in #209136 and you sending the prompt continuation in #210615, to handle that, but it's not finished yet

[Tyriar]

Yeah was thinking about sending over the full prompt but there's probably lots of edge cases around escapes in it for each shell. Just the terminator is a pretty good idea.

Ive also been toying with the idea of learning what the prompt is over 3+ prompts, but the initial ones wouldn't benefit