This adds the ability to import exception into a module at instantiation
time. Only a {WasmExceptionObject} that has been exported by another
module instance can be imported, all other values are rejected.

Note that currently there is no signature check being performed to make
sure the imported exception matches the expected type. Also the identity
of imported exceptions is not yet preserved.

Furthermore the engine does not yet match thrown exception objects on a
global level across modules. Hence imported exceptions will (wrongly)
behave as completely new types within the module.

R=clemensh@chromium.org
TEST=mjsunit/wasm/exceptions-import,unittests/WasmModuleVerifyTest
BUG=v8:8091

Change-Id: If247762b949a1ba4a87d13bc3e790a45dbc67815
Reviewed-on: https://chromium-review.googlesource.com/1216402
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55777}