Previously we'd treat %_AsyncFunctionReject (and %AsyncFunctionReject)
as side-effect free (in async functions), but that's not correct, since
promise rejections have side-effects (at the very least triggering the
unhandled promise rejection machinery in the browser).

This required a minor refactoring as previously we'd classify functions
as side-effecting or not depending on whether they contain any calls to
side-effecting intrinsics, no matter whether this call is actually
executed or not. That would break REPL mode however if we'd generally
treat all async functions with %_AsyncFunctionReject intrinsic calls as
side-effecting, so instead of performing the intrinsic checks ahead of
time, we now perform the test at execution time.

Before: https://imgur.com/5BvJP9d.png
After: https://imgur.com/10FanNr.png
Fixed: chromium:1249275
Change-Id: Ib06f945ba21f1e06ee9b13a1363fad342464fd9a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3197712
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>
Auto-Submit: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77183}