📜scrollback search highlight 1️⃣ is incorrect, and 2️⃣ incorrectly snaps in response to STDOUT

### Windows Terminal version

1.23.3232.0

### Windows build number

10.0.19045.5247

### Other Software

### Steps to reproduce

1) Hit Ctrl-Shift-F while a script is generating output

2) Enter in something to search for. I suggest “e” for bug-finding purposes.

3) Watch the highlights incorrectly dance around the screen.
4) Fail to ever find your highlighted text as long as a script is running.

### Expected Behavior

1) The highlights to what I am searching for are only displayed on top of what I am searching for.

2) If I am in search/scrollback mode and more STDOUT happens, it doesn’t snap me anywhere. (currently it snaps me all over the place)

Side-note: You know what else would be nice? A pause button that suspends the process temporarily. So we can go back and find our error message before it scrolls off-buffer.

### Actual Behavior


Start by reproducing the Ctrl-Shift-F search and scrollback behavior while a script continuously generates STDOUT, using the listed Windows Terminal and Windows build versions. Trace the search/scrollback flow responsible for highlight positioning and viewport movement; done means highlights remain over matching text and new STDOUT does not move the view while search mode is active.

Written by the indexing model from the issue text.