This commit adds lots of plumbing to get the type section from the module linking proposal plumbed all the way through to the `wasmtime` crate and the `wasmtime-c-api` crate. This isn't all that useful right now because Wasmtime doesn't support imported/exported modules/instances, but this is all necessary groundwork to getting that exported at some point. I've added some light tests but I suspect the bulk of the testing will come in a future commit. One major change in this commit is that `SignatureIndex` no longer follows type type index space in a wasm module. Instead a new `TypeIndex` type is used to track that. Function signatures, still indexed by `SignatureIndex`, are then packed together tightly.
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.