This commit adds initial (gated) support for the multi-memory wasm proposal. This was actually quite easy since almost all of wasmtime already expected multi-memory to be implemented one day. The only real substantive change is the `memory.copy` intrinsic changes, which now accounts for the source/destination memories possibly being different.
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.
Most users will want to use the main wasmtime crate instead of using this
crate directly.