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/wiggle/generate/src/wasmtime.rs

@@ -121,11 +121,7 @@ fn generate_func(
         let (mem , ctx) = mem.data_and_store_mut(&mut caller);
         let ctx = get_cx(ctx);
         let mem = #rt::wasmtime::WasmtimeGuestMemory::new(mem);
-        match #abi_func(ctx, &mem #(, #arg_names)*) #await_ {
-            Ok(r) => Ok(<#ret_ty>::from(r)),
-            Err(#rt::Trap::String(err)) => Err(#rt::wasmtime_crate::Trap::new(err)),
-            Err(#rt::Trap::I32Exit(err)) => Err(#rt::wasmtime_crate::Trap::i32_exit(err)),
-        }
+        Ok(<#ret_ty>::from(#abi_func(ctx, &mem #(, #arg_names)*) #await_ ?))
     };
 
     match asyncness {