Introduce new operator LoadTransform that holds a LoadTransformInfo param,
which describes the kind of load (normal, unaligned, protected), and a
transformation (splat or extend, signed or unsigned).

We have a new method that a full decoder needs to implement, LoadTransform,
which resuses the existing LoadType we have, but also takes a LoadTransform,
to distinguish between splats and extends at the decoder level.

This implements 4 out of the 10 suggested load splat/extend operations
(to keep the cl smaller), and is also missing interpreter support (will
be added in the future).



Change-Id: I1e65c693bfbe30e2a511c81b5a32e06aacbddc19
Bug: v8:9886
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1863863Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64819}