Similar to https://crrev.com/c/3634781, this switches some {BitVector}s
in the regular top-tier register allocator to {SparseBitVector}. For
functions with a huge amount of virtual registers, this would save a
significant amount of memory, and also performance.

For small number of registers though we probably introduce a slight
regression, because there is one more dynamic check to be performed
before accessing the bits.

R=mslekova@chromium.org

Bug: chromium:1313379, v8:12780
Change-Id: Ib65d22ad0a8e2c933f7178f4fefc36e500be623c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3650602Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80806}