Massive memory leak if left in a scrolled up position

### Windows Terminal version

1.24.11321.0

### Windows build number

26200.8655

### Other Software

### Steps to reproduce

Leave a console program in a scrolled up position for an hour two whilst it continues to emit lines of output.

After a while, Windows Terminal will consume all available memory.

If you press a key to get it to scroll down, there will be a long delay and then the memory gets released and everything returns to normal.

It's just text. There is no reason it should require gigabytes of memory to hold a buffer of some text.

### Expected Behavior

No noticeable impact on memory usage. Or, if this behaviour is intentional, then put limits on it so that once memory usage exceeds a certain threshold it will automatically scroll back down to avoid rinsing the machine.

### Actual Behavior

Memory is kept allocated until scrolled back down.

Start by reproducing the report on Windows Terminal 1.24.11321.0 with a console program continuously emitting output while the viewport remains scrolled up. The payload names no source file or test, so trace the output and scroll-buffer handling first. Done means memory remains bounded during the hour-long scenario and scrolling back down does not cause a long recovery delay.

Written by the indexing model from the issue text.