This adds support for the `table.copy` instruction from the bulk memory proposal. It also supports multiple tables, which were introduced by the reference types proposal. Part of #928
This is the wasmtime-runtime crate, which contains wasm runtime library
support, supporting the wasm ABI used by wasmtime-environ,
wasmtime-jit, and wasmtime-obj.
This crate does not make a host vs. target distinction; it is meant to be compiled for the target.