Implement resource support in Wasmtime's `bindgen!` macro

[alexcrichton]

This is an issue to track the implementation and support for the WIT resource type in the bindgen! macro for Wasmtime. Completing this will require #6691 to land first as it requires all the groundwork there, but it theoretically won't be too hard after that.

[alexcrichton]

This was done some time ago.