Implements the **FTCS_PROMPT** sequence, `OSC 133 ; A ST`. In this PR, it's just used to set a simple Prompt mark on the current line, in the same way that the iTerm2 sequence works.
There's rumination in #11000 on how to implement the rest of the FTCS sequences.
This is broken into its own PR at the moment. [Quoth j4james](https://github.com/microsoft/terminal/pull/12948#issuecomment-1136360132):
> That should be just as easy, and I've noticed a couple of other terminals that are doing that, so it's not unprecedented. If we don't have any immediate use for the other options, there shouldn't be any harm in ignoring them initially.
>
> And the benefit of going with the more widely supported sequence is that we're more likely to benefit from any shells that have this functionality built in. Otherwise they're forced to try and detect the terminal, which is practically impossible for Windows Terminal. Even iTerm2 supports the `OSC 133` sequence, so we'd probably be the only odd one out.
This part of the plumbing is super easy, so I thought it would be valuable to add regardless if we get to the whole of FTCS in 1.15.
* [x] I work here
* [x] Tested manually - in my pwsh `$PROFILE`:
```pwsh
function prompt {
$loc = $($executionContext.SessionState.Path.CurrentLocation);
$out = "PS $loc$('>' * ($nestedPromptLevel + 1)) ";
$out += "$([char]27)]9;9;`"$loc`"$([char]07)";
$out += "$([char]27)]133;A;$([char]7)"; # add the FTCS_PROMPT to the... well, end, but you get the point
return $out
}
```
* See also #11000
f685720cac