gpui: Clear the element arena after presenting the frame (#33338)
This is an easy way to shave some microseconds off the critical path for
frame rendering. On my machine this reduces typical frame rendering
latency by ~100 microseconds, probably quite a bit more on slower
machines.
Here is how long it typically takes to drop elements from the arena,
from a fairly brief run:

Release Notes:
- N/A
9427526a41Michael Sloan committed on 6/24/2025, 7:43:33 PM· committed by GitHubparenteec26c9