This CL introduces two MachineTypes - SignedBigInt64 and UnsignedBigInt64, which are represented as Word64 but will be rematerialized to BigInt in deoptimization. This will avoid unnecessary conversions for BigInt64s when they are passed to StateValues.

Bug: v8:9407
Change-Id: I65fdee3e028ed8f9920b1c20ff78993c7784de48
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3858238Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Qifan Pan <panq@google.com>
Cr-Commit-Position: refs/heads/main@{#83230}