Pause outputting lines when the user is selecting text

[almonk]

Problem:
It always bugs me when i start copying something out the terminal but some ongoing process keeps outputting newlines AS i'm trying to select something.

Proposed solution:
Ghostty buffers new lines while mouseDown and gives some sort of UI indication that there are newlines being collected in the background.

When the user fires mouseUp, and the selection has stopped, the collected lines are output but the scroll position does not change so as not to create a jarring experience. Autoscrolling should re-engage if the user scrolls to the tail of output.

[tristan957]

AdwToast would be a perfect UI solution for this on the libadwaita side.

[mitchellh]

As a simplification initially, we can show an icon (that's clickable) that more lines simply exist. Counting the number of lines introduces a bunch of unnecessary complexity to initially ship this improvement.