This adds support for loading, compiling, linking, and running components which
use the [Async
ABI](https://github.com/WebAssembly/component-model/blob/main/design/mvp/Async.md)
along with the [`stream`, `future`, and
`error-context`](WebAssembly/component-model#405) types.
It also adds support for generating host bindings such that multiple host
functions can be run concurrently with guest tasks -- without monopolizing the
`Store`.

See the [implementation RFC](bytecodealliance/rfcs#38)
for details, as well as [this
repo](https://github.com/dicej/component-async-demo) containing end-to-end smoke
tests.

This is very much a work-in progress, with a number of tasks remaining:

- [ ] Avoid exposing global task IDs to guests and use per-instance IDs instead
- [ ] Track `task.return` type during compilation and assert the actual and expected types match at runtime
- [ ] Ensure all guest pointers are bounds-checked when lifting, lowering, or copying values
- [ ] Reduce code duplication in `wasmtime_cranelift::compiler::component`
- [ ] Reduce code duplication between `StoreContextMut::on_fiber` and `concurrent::on_fiber`
- [ ] Minimize and/or document the use of unsafe code
- [ ] Add support for `(Typed)Func::call_concurrent` per the RFC
- [ ] Add support for multiplexing stream/future reads/writes and concurrent calls to guest exports per the RFC
- [ ] Refactor, clean up, and unify handling of backpressure, yields, and even polling
- [ ] Guard against reentrance where required (e.g. in certain fused adapter calls)
- [ ] Add integration test cases covering new functionality to tests/all/component_model (starting by porting over the tests in https://github.com/dicej/component-async-demo)
- [ ] Add binding generation test cases to crates/component-macro/tests
- [ ] Add WAST tests to tests/misc_testsuite/component-model
- [ ] Add support and test coverage for callback-less async functions (e.g. goroutines)
- [ ] Switch to back to upstream `wasm-tools` once bytecodealliance/wasm-tools#1895 has been merged and released

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

fix clippy warnings and bench/fuzzing errors

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

revert atomic.wit whitespace change

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

fix build when component-model disabled

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

bless component-macro expected output

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

fix no-std build error

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

fix build with --no-default-features --features runtime,component-model

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

partly fix no-std build

It's still broken due to the use of `std::collections::HashMap` in
crates/wasmtime/src/runtime/vm/component.rs.  I'll address that as part of the
work to avoid exposing global task/future/stream/error-context handles to
guests.

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

maintain per-instance tables for futures, streams, and error-contexts

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

refactor task/stream/future handle lifting/lowering

This addresses a couple of issues:

- Previously, we were passing task/stream/future/error-context reps directly to
  instances while keeping track of which instance had access to which rep.  That
  worked fine in that there was no way to forge access to inaccessible reps, but
  it leaked information about what other instances were doing.  Now we maintain
  per-instance waitable and error-context tables which map the reps to and from
  the handles which the instance sees.

- The `no_std` build was broken due to use of `HashMap` in
  `runtime::vm::component`, which is now fixed.

Note that we use one single table per instance for all tasks, streams, and
futures.  This is partly necessary because, when async events are delivered to
the guest, it wouldn't have enough context to know which stream or future we're
talking about if each unique stream and future type had its own table.  So at
minimum, we need to use the same table for all streams (regardless of payload
type), and likewise for futures.  Also, per
WebAssembly/component-model#395 (comment),
the plan is to move towards a shared table for all resource types as well, so
this moves us in that direction.

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

fix wave breakage due to new stream/future/error-context types

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

Signed-off-by: Joel Dice <joel.dice@fermyon.com>

We can't statically verify a given call to `task.return` corresponds to the
expected core signature appropriate for the currently running task, so we must
do so at runtime.  In order to make that check efficient, we intern the types.

My initial plan was to use `ModuleInternedTypeIndex` and/or `VMSharedTypeIndex`
for interning, but that got hairy with WasmGC considerations, so instead I added
new fields to `ComponentTypes` and `ComponentTypesBuilder`.

Signed-off-by: Joel Dice <joel.dice@fermyon.com>