Interpreter: Add bitwise shift operators

These only support fixed shift amounts (for now) ... because that's what
skvx supports ... because that's what various SIMD instructions support.

(We could loop over lanes, but the only need for this at the moment
is fine with constant shift).

Change-Id: I0e2c17084d019ff9b9a21476633adb59b3ce4bd6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/243656
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
4 files changed