This adds support for multiple catch blocks being attached to a single
try block. The implemented semantics are that type checks are performed
in order from top to bottom.

Note that multiple catch blocks of the same type are not prohibited and
will be accepted, making the second such block essentially unreachable.
The current proposal neither explicitly allows nor prohibits it.

R=clemensh@chromium.org
TEST=mjsunit/wasm/exceptions
BUG=v8:8091

Change-Id: I31e7a07a7cffdd909a58342e00f05e52ed1a3182
Reviewed-on: https://chromium-review.googlesource.com/c/1270591Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56478}