c-api: component-model: An "unchecked" way of calling a function

Currently funciton invocations, both on the host and that of guests, go through `wasmtime_component_val_t` which is a bit of a heavyweight representation of arguments/results in the component model. Ideally the C API sould support something like `wasmtime_func_call_unchecked` which places more burden on the caller but is implemented in a much more efficient fashion. Supporting this with the full matrix of types in the component model is unclear how it will be done so this is, to me at least, an open design/research question currently without a solution.