The previous change to JSCallReducer::ReduceCallApiFunction regressed
the case a bit where the optimized graph has some knowledge about the
receiver already, but the API callback didn't need any receiver checks,
as in that case we unnecessarily added a ConvertReceiver node. This
change refactors the code to first see if there's information in the
graph about the receiver, and only if none is found, introduce the
ConvertReceiver node.

It also removes the unnecessary context load from the target function,
since the API callback doesn't care about the concrete context, and
we never inline cross native contexts, so using whatever incoming
context we have is perfectly fine (and saves us from unnecessarily
materializing the target just to load the native context off of it).

Drive-by-fix: Remove bogus comment about CallApiCallbackStub parameters.

Bug: v8:8820
Change-Id: Ide1b283d9e448c3f0ae8f2daf4b1ad0202eae09e
Cq-Include-Trybots: luci.chromium.try:linux-blink-rel
Reviewed-on: https://chromium-review.googlesource.com/c/1466881
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59536}