Add ResourceLimiterAsync, which can yield until resource is available

[pchickey]

This PR:

• Moves ResourceLimiter's definition from wasmtime_runtime to wasmtime
• Adds an additional ResourceLimiterAsync, which is just like a ResourceLimiter except the memory_growing and table_growing methods are async (via #[async_trait]). This is so that async embeddings of wasmtime can handle memory or table growing by awaiting for a resource to be available.
• In order for the ResourceLimiterAsync methods to await inside memory & table grows, we need to add async variants of Memory::new, Memory::grow, Table::new, and Table::grow. These variants are not required for all async Stores, only for stores which are given a Store::limiter_async. So, this won't break any existing code.
• Both ResourceLimiter traits now get table_grow_failed, which corresponds to memory_grow_failed. Better to just get this over with now than have to add it in later.
• Test suite covers table limiting and async and panics now.

I had to restructure a fair bit of the interface between runtime and wasmtime for this PR, including extending the wasmtime_runtime::Store trait, and changing the error type passed between them to anyhow::Error instead of Box<dyn std::error::Error + Send + Sync>.

Additionally, both ResourceLimiters are now safer: wasmtime_runtime now catches any panics that occur from the user's impl of the traits.

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[alexcrichton]

Looking good to me! If you're up for it I think it would also be interesting to have tests which panic! in the memory growth (either in the async or sync version) from the custom trait implementation which then asserts that the panic can be caught from the other side of wasm and handled.

[alexcrichton]

All looks good to me! A few minor things I might also ask for:

• Doc updates to the blocking methods that they can panic for async stores with an async limiter configured
• Could you add a test where the async-ness is exercised as well? I noticed most of them using the async trait were just async conditions, but could there be one which also sleeps or synchronizes with some other task or something like that?

[alexcrichton]

👍

Ok final nit I forgot from earlier, can you add this to the #[cfg]'d APIs so the feature requirement is rendered with rustdoc? Other than that looks good to go!

#[cfg_attr(nightlydoc, doc(cfg(feature = "async")))]