Define a macro in code-generator-x64 to help identify cases when the
shift value is an immediate/constant. In those cases we can directly
emit the shifts without any masking, since the instruction selector
would have modulo-ed the shift value. We also don't need any temporaries
in this case.

This is only x64 codegen, optimizations for other archs will come in
future patches (and will probably look very similar to this).

The current test case passes the shifts as an immediate, so we add a new
path that loads the shift value from memory, thereby exercising the
slower path of non-immediate shift value.

Bug: v8:10115
Change-Id: Iaf13d81595714882a8f5418734e031b8bc654af3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2026067Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66074}