* wasmtime component bindgen: when tracing is enabled, emit an event for arguments and results
This is consistient with what wiggle does (see
https://github.com/bytecodealliance/wasmtime/blob/main/crates/wiggle/generate/src/funcs.rs#L266), with the exceptions that
1. wiggle has a facility for disabling tracing on a per-function basis,
a requirement which was driven by functions which pass secrets into wasm. this will be added to wasmtime-wit-bindgen at a later date.
2. wiggle doesn't actually emit an event when calling a function which
takes no arguments (see `&& func.params.len() > 0` in predicate), in
this case we emit an event with the body `"call"`, to ensure these calls
are observable.
* review feedback: add call and return messages to events
* consistiency: dont drop `guest` from `wit-bindgen guest export` in span
cc1c14ac91