One way to call and register functions #1997

Each operation has several entry points with different costs:

• Host calls: call, and the deprecated call_guest_function_by_name.
• Guest calls to the host: call_host, and call_host_function, which takes an owned Vec<ParameterValue>.
• Guest registration: #[guest_function], register_fn, and register_function with a hand-built definition.

Proposal:

• Remove call_guest_function_by_name.
• Add guest call_host_dynamic(name, &[ParameterValueRef], ReturnType) for runtime signatures. Deprecate call_host_function.
• Deprecate register_function and print_output_with_host_print. Switch WIT codegen to register_fn.

Builds on #1987.