[Wasm] Reference types

Tracking: WebAssembly [reference types][r] proposal is attempting to go to Phase 4. Obviously it is not going to be trivial amount of work to implement. Upside of trying to this proposal is that it is in a mature stage and won't change much. It might also be useful for embedded scenarios.

[r]: https://github.com/WebAssembly/reference-types

The issue names no files, tests, or entry points. Start by reading the linked WebAssembly reference-types proposal and locating ChakraCore's existing WebAssembly implementation; completion would require implementing the proposal, but the issue does not define a narrower scope or validation plan.

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