From several runtime functions, this was still missing. For some, it
shouldn't really matter, but some runtime functions (e.g. DebugBreak)
can call back into JS to wasm, and there it matters.

As it never hurts to clear and re-set the flag, this CL consistently
resets the flag for all runtime functions called from wasm code. For
runtime functions that are called from outside of wasm (e.g. from
wrappers), we add a DCHECK instead that the flag is not set. There is
one exception (WasmThrowTypeError), which is called both from wasm code
and from wrappers. In this case it's OK, I added a comment saying why.

Drive-by: Remove obsolete comments (from a time where this clearing
was still optional in some cases).

R=ahaas@chromium.org

Bug: v8:10389
Change-Id: Id4ec92a42e89005276b42c145fe3572eb459d220
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2157026Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67274}