Significantly reduces the number of blocks in CSA code generated by
Torque by merging blocks along a straight-line path into a single
block.

Bug: v8:9861
Change-Id: I592cc1ed5b1ca0ad12c907d5cce7dcf7fec5f141
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1917157
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65181}