maintainer note: hijacking thread to track bugs we need to fix before enabling marks for Stable builds

See also: #11000

### Tasks
- [ ] #14792
- [ ] #15426
- [x] Make sure ED2 works to clear/move marks
- [x] Same with ED3 for clearing scrollback
- [x] "Clear buffer" action too
- [x] `cls` too
- [x] `clear-host` too
- [ ] Make sure marks reflow on resize
- [ ] Remove `experimental.` from settings
- [ ] Remove it from `features.xml`
- [x] Rudimentarily optimize rendering, ala https://github.com/microsoft/terminal/pull/14045#discussion_r1262965690
- [ ] https://github.com/microsoft/terminal/issues/15813
- [ ] https://github.com/microsoft/terminal/issues/15955
- [ ] Hitting enter in the middle of a command will mark the middle as the end of the command (not the actual end of the command)

Windows Terminal version

1.16.10262.0

Windows build number

10.0.22621.0

Other Software

I am attempting to add a scroll mark, which I believe should appear as a notch on the scroll bar, per #12948.

No method to create a scroll mark results in a visible notch in the scroll bar.

I have "experimental.showMarksOnScrollbar": true enabled on my profile

Steps to reproduce

Attempt 1 - echo (what I want so I can make my prompt auto-mark)

The docs have a screenshot of the relevant text rather than characters:

I had to OCR the above image, and I've checked it a couple of times after @ / 0 being switched, but I'm relatively sure it is:

echo -e 'Mark this Line\x1b]1337;SetMark\x07'

I have "experimental.showMarksOnScrollbar": true enabled on my profile but it doesn't seem to work. I expected a mark on the scroll bar. to appear after running this command.

Attempt 2 - do... something I don't understand

There is also this animated GIF (see docs for animation).

I do not understand how echo "mark 1" is making a mark. The docs mention there is an addMark action but I do not understand how mark 1 and mark 2 etc are related to the addMark action.

Run 'Add Mark' action manually.

I have tried running the AddMark action manually as well:

again I can't get marks to appear. Windows Terminal 1.16.10262.0.

Thanks for understanding - I'm really excited to try this feature, and I appreciate you creating it. ❤️

Expected Behavior

Get a small notch on the scroll bar

Actual Behavior

The scroll bar remains unchanged.