This CL refactors the handling of metadata associated with WebAssembly
modules to reduce the duplicate marshalling of data from the C++ world
to the JavaScript world. It does this by wrapping the C++ WasmModule*
object in a Foreign that is rooted from the on-heap WasmCompiledModule
(which is itself just a FixedArray). Upon serialization, the C++ object
is ignored and the original WASM wire bytes are serialized. Upon
deserialization, the C++ object is reconstituted by reparsing the bytes.

This is motivated by increasing complications in implementing the JS
API, in particular WebAssembly.Table, which must perform signature
canonicalization across instances.

Additionally, this CL implements the proper base + offset initialization
behavior for tables.

R=rossberg@chromium.org,bradnelson@chromium.org,mtrofin@chromium.org,yangguo@chromium.org
BUG=v8:5507, chromium:575167, chromium:657316

Review-Url: https://chromiumcodereview.appspot.com/2424623002
Cr-Commit-Position: refs/heads/master@{#40434}