[wasm-gc] Implement optional-depth rtts

As per the latest wasm-gc spec, rtts now have optional depth, with
(rtt n type) <: (rtt type) for every depth n. Liftoff compilation for
type checks without depth are not supported yet.

Bug: v8:7748
Change-Id: I4971875e6a42db6d333b61ca5e2996e875f39f60
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2649043


Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Manos Koukoutos <manoskouk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72395}