This implements the editorial change in https://github.com/tc39/ecma262/pull/1146
which removes the need to allocate the throwaway promise in await (the throwaway
promise was not exposed to user JavaScript anyways, but this spec change allows
us to rely on this behavior). Now we still need the throwaway promise for proper
before and after events with both DevTools (which might change) and PromiseHooks.
So if either DevTools or PromiseHooks is on, we call into %AwaitPromisesInit,
which then allocates the throwaway promise and does all the other debugger/hooks
related setup.

This gives around 7% improvement on the doxbee-async-es2017-native and around 1-2%
on the parallel-async-es2017-native benchmarks.

Bug: v8:7253, v8:8285
Ref: tc39/ecma262#1146
Tbr: ulan@chromium.org
Change-Id: I972ba0538ec8c00808e95b183603025c7e55a6d3
Cq-Include-Trybots: luci.chromium.try:linux_chromium_headless_rel;luci.chromium.try:linux_chromium_rel_ng;master.tryserver.blink:linux_trusty_blink_rel
Reviewed-on: https://chromium-review.googlesource.com/c/1270798
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56506}