Add a new fuzzer focused on component-model-async events

[alexcrichton]

This commit adds a new fuzzer mode to the misc fuzzer of Wasmtime which is focused on async events and interleavings of components using the component-model-async proposal. This fuzzer works by having a precompiled guest program which serves as the component to run. This precompiled component has a custom fuzz.wit which is used to interface with the fuzzer itself. The fuzzer is then a fuzz-generated sequence of commands to send to the component which verifies that everything executes correctly, has no panics, etc.

This fuzzer intends to stress async communication and task infrastructure with component-model-async. Notably this does not stress lifting/lowering or arbitrary type signatures. This does, however, permute all of the following:

• Guest/host interactions (also guest/guest, host/host, etc).
• Async functions, both ready and pending.
• Future operations: reads, writes, cancellation, transfers, etc.
• Stream operations: reads, writes, cancellation, transfers, etc.

This is all throwing into a large "soup" and then asserted to work correctly. There's a few gotchas here and there for how this fuzzer is designed, such as some events requiring "yield N times to await this event happening". This is required because Wasmtime is allowed to non-deterministically select between a number of "ready events" and what to dispatch.

This is not intended to be a one-size-fits-all fuzzer for component-model-async. The recent enhancements to the component_api fuzzer are intended to complement this fuzzer in terms of what's stressed where internally.

[alexcrichton]

Currently leaving this in draft form while bytecodealliance/wit-bindgen#1446 is pending.

[alexcrichton]

I'll also note that I understand this is a pretty meat and pretty dense fuzzer, so I'm happy to walk through it if @dicej you or anyone else is interested. I'm also happy to write up more docs anywhere as necessary. Current docs are primarily located at crates/test-programs/src/bin/fuzz_async.rs

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