This is identical to https://crrev.com/c/3094011, but for 16-bit values.
We introduce another instruction to differentiate between 16->32 bit
sign extensions and 16->64 bit sign extensions.

R=ahaas@chromium.org, mslekova@chromium.org

Bug: chromium:1239116
Change-Id: I2742e9d9c2b4a038fc7a0b1715faf8f25fa20b1f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3094012
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76284}