For short inputs (<= size of the type we want to generate), we fell back
to just generating constants. This CL changes that to only fall back to
constants once a single byte remains, and adds options to use constants
already before that.

R=ahaas@chromium.org

Bug: v8:894307
Change-Id: Ic4bf05d06090f52b67de2b322a9d5dcab6bbbe39
Reviewed-on: https://chromium-review.googlesource.com/c/1337739Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57573}