Initial fixed-length list implementation

[cpetig]

See WebAssembly/component-model#384 for the commit which added fixed size lists to the component model standard documents.

[cpetig]

I have a newer version at https://github.com/cpetig/wit-bindgen/tree/work-in-progress which tests more in depth and also supports C++, I need to separate and clean up that one and then push it here for review.

[cpetig]

Also this requires bytecodealliance/wasmtime#10619 , and a very recent version of wasm-component-ld for the tests to pass.

[cpetig]

This is ready, but depends on bytecodealliance/wasmtime#10619 for successful tests.

[alexcrichton]

Looks good to me!

[cpetig]

This still has a limitation: The generated Rust and C++ code can't handle non-Copy/POD types. For Functional Safety this isn't an issue as you need to avoid putting string or list into a fixed size array anyway, resources might still make some sense.

I created #1501 to track this limitation.

[cpetig]

TODO: Check for correct usage of "fixed-length" over "fixed-size"

[cpetig]

I guess I should fix the naming in wasm-tools (fixed length list) before merging this MR (as it shouldn't be urgent), but on the other hand that merge will affect all of wit-bindgen languages anyway.

Second thought: The impact of the wasm-tools change will be identical (all code generators in wit-bindgen have to do a search and replace independently of whether this patch is merged or not). But it will create a conflict with this patch, so I guess it can be merged and then the other change can be discussed separately.

[cpetig]

The (discussion of the) rename in wasm-tools happens in bytecodealliance/wasm-tools#2421

[alexcrichton]

Let's go ahead and get this merged and renames/refactors can land in parallel