This adjusts the RunMicrotask logic to invoke CallHandlerInfo microtasks
from CSA land directly (via a runtime function call), instead of bailing
out to C++ for the rest of the microtask queue entries. Even in simple
micro-benchmarks there doesn't seem to be a huge performance difference.
In fact performance get's better when CallHandlerInfo and promises are
mixed, which makes sense, since calling from C++ to JS land is more
expensive than the other way around.

But just in case the runtime function call overhead ever becomes the
bottleneck we can introduce a direct C++ call and setup a handle scope
around it, much like a very simple version of CallApiFunctionStub.

This greatly simplifies the microtask handling and paves the way for
refactoring the queue to significant reduce the GC overhead associated
with promises currently.

Bug: v8:7253
Change-Id: I33adb62a6bada138674d324f36d4be894e27f3c9
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/890441Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50934}