Testing #145629

Could repro this slowness by filling the buffer and then searching for a single letter, this is on a 12th gen i7 (fast modern CPU):

A similar thing happens when pressing enter in this state since we don't do any diffing, just clear and re-render.

Ideas to explore:

• Move from rendering each decoration to calculating colored zones which merge similar rectangles into the same zone and render them
• If the buffer is full, explore shifting the texture up depending on how much scrolling occurs (might be tricky to get right)