Adds missing opcodes for exception handling for the function body decoder.
Also adds error messages if the exception handling construct is not yet
functional.

Note that the previous prototype for catch and throw have been marked
as not yet functional. This was done because it doesn't model
exceptions the way the proposal suggests. Rather, they implement a
hard-coded (c++ model) of exceptions.

Bug: v8:6577
Change-Id: Ife170b9f0cb2be91b11082e43c4795ce81a427dc
Reviewed-on: https://chromium-review.googlesource.com/564138Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Karl Schimpf <kschimpf@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46540}