wiggle: make wasmtime a mandatory dep, get rid of own Trap enum (#5137)

* wiggle: no longer need to guard wasmtime integration behind a feature

this existed so we could use wiggle in lucet, but lucet is long EOL

* replace wiggle::Trap with wiggle::wasmtime_crate::Trap

* wiggle tests: unwrap traps because we cant assert_eq on them

* wasi-common: emit a wasmtime::Trap instead of a wiggle::Trap

formally add a dependency on wasmtime here to make it obvious, though
we do now have a transitive one via wiggle no matter what (and therefore
can get rid of the default-features=false on the wiggle dep)

* wasi-nn: use wasmtime::Trap instead of wiggle::Trap

there's no way the implementation of this func is actually
a good idea, it will panic the host process on any error,
but I'll ask @mtr to fix that

* wiggle test-helpers examples: fixes

* wasi-common cant cross compile to wasm32-unknown-emscripten anymore

this was originally for the WASI polyfill for web targets. Those days
are way behind us now.

* wasmtime wont compile for armv7-unknown-linux-gnueabihf either

crates/wasi-nn/src/witx.rs

@@ -11,7 +11,10 @@ wiggle::from_witx!({
 use types::NnErrno;
 
 impl<'a> types::UserErrorConversion for WasiNnCtx {
-    fn nn_errno_from_wasi_nn_error(&mut self, e: WasiNnError) -> Result<NnErrno, wiggle::Trap> {
+    fn nn_errno_from_wasi_nn_error(
+        &mut self,
+        e: WasiNnError,
+    ) -> Result<NnErrno, wiggle::wasmtime_crate::Trap> {
         eprintln!("Host error: {:?}", e);
         match e {
             WasiNnError::BackendError(_) => unimplemented!(),