[wasm] Use checked casts for builtins where possible.

This makes sure that proper checked casts (i.e. {CAST} instead of the
unsafe {UncheckedCast} before) are used for all WebAssembly runtime
stubs. This is possible because the corresponding builtins are embedded
and hence can use proper assertion mechanisms.

R=clemensb@chromium.org
BUG=v8:10021

Change-Id: I344ae8ba7dd4c5d3f5dc2467f7d58b93517d9af7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1940264
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65236}