This fixes crashes during validation when trying to construct modules
with excessively large function tables. The {WasmModuleBuilder} now
gracefully checks against existing WebAssembly implementation limits.

R=clemensh@chromium.org
TEST=mjsunit/regress/regress-crbug-715455
BUG=chromium:715455

Change-Id: Ia9738cb0b49a1eb4caf073b75301c0303f295699
Reviewed-on: https://chromium-review.googlesource.com/509530
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45429}