Up until now, we cached export wrappers per export index. With the
anyref proposal potentially many more functions will need export
wrappers, e.g. any function that is stored in a table, and any
function accessed by the new ref.func instruction.

With this CL, we change the caching scheme an do the caching per
signature. Thereby we can guarantee that any export wrapper which
potentially exists can be stored in the cache.

For cctests which use wasm-run-utils, we don't know the size of the
cache anymore ahead of time. However, we assume that no more than
5 signatures will be used in any cctest. If this assumption is not
true, we can just adjust the number.

The cache is now accessed in all code paths where we need an export
wrapper.

Bug: chromium:962850

Change-Id: I32df60dfa7801d1e71f7d837da091f388198af1f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1615247
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61752}