Emitting bytes to the Uint8Array directly speeds up generation of
binaries enormously.
On the limits-any.js spec test (which creates huge modules), the
execution time of an optdebug build reduces from 286 seconds to 61
seconds.

R=titzer@chromium.org
CC=​ahaas@chromium.org, ssauleau@igalia.com

Change-Id: I5b473b7dc7b0853e54d2406f3db3658bb2abed40
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1508352Reviewed-by: Ben Titzer <titzer@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60096}