This change:
1. Updates the Torque compiler to allow direct access to bitfields that
   are packed within Smi values, which previously would have required a
   separate untagging step,
2. Updates JSRegExpStringIterator to represent its flags in Torque,
3. Adds reduction cases in MachineOperatorReducer for when the input to
   a branch or the left-hand side of a Word32Equals is based on a 64-bit
   shift-and-mask operation which has been truncated to 32 bits, as is
   the case in the code generated by step 1, and
4. Adds a reduction case in MachineOperatorReducer to remove an extra
   Word64And operation added by step 1.

Bug: v8:7793
Change-Id: Ib4ac2def6211b3cae6be25a8b2a644be5c7d6d3f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2119225
Commit-Queue: Seth Brenith <seth.brenith@microsoft.com>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67290}