This adds the ability to add exception types to the export section of a
module and reference them via the local exception index. Currently the
export object then just contains the local index as a number, which is
only temporary until we have proper export wrappers for exceptions.

Also note that this tightens the restriction for the modules exception
section to be located in between the import and the export section.

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

Change-Id: Ie26081c3f94e71cb576057db7e45ec5bd0e112f9
Reviewed-on: https://chromium-review.googlesource.com/1206873
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55679}