This commit splits out a `FiberStack` from `Fiber`, allowing the instance allocator trait to return `FiberStack` rather than raw stack pointers. This keeps the stack creation mostly in `wasmtime_fiber`, but now the on-demand instance allocator can make use of it. The instance allocators no longer have to return a "not supported" error to indicate that the store should allocate its own fiber stack. This includes a bunch of cleanup in the instance allocator to scope stacks to the new "async" feature in the runtime. Closes #2708.
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.