dillon1000/react

Lower Suspense throttling heuristic to 300ms (#26803)

Now that the throttling mechanism applies more often, we've decided to
lower this a tad to ensure it's not noticeable. The idea is it should be
just large enough to prevent jank when lots of different parts of the UI
load in rapid succession, but not large enough to make the UI feel
sluggish. There's no perfect number, it's just a heuristic.