This adds type reflection support to the {WebAssembly.Module.exports} as
well as {WebAssembly.Module.imports} method. It also refactors existing
reflective code to use the internal instead of the public embedder API,
which is slightly more efficient anyways.

R=ahaas@chromium.org
TEST=mjsunit/wasm/type-reflection
BUG=v8:7742

Change-Id: I88a6c7e9236a549808707c72e40a63302b7747a9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1763527Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63312}