Plumb (implements "...") support throughout

[alexcrichton]

This commit plumbs the type system support for (implement "...") in
the component model throughout Wasmtime. Notably the fields and such are
all faithfully carried over from wasmparser into the type reflection
within Wasmtime itself. This'll be needed for loading components with
this field. Note that no bindings generation is not updated yet, this is
only the compiler/runtime side of (implement "...") and bindings
generation will be a subsequent update.

[alexcrichton]

Note that this is currently built on #13360

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