I noticed that the generated code from the Torque macro
EnsureArrayLengthWritable included an imul instruction, even though the
inputs to that instruction are both constants. This change adds the
ability for MachineOperatorReducer to get rid of that operation.

Change-Id: Ia2050c888d76f110d1290fd9eab13853c3353a63
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1941138
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65310}