wasi-common: switch all logs from log to tracing

tracing is already the dep that wiggle uses.

I used tracing structured arguments wherever I could, but I skipped over
it in all of the snapshot_0 code, because I'm going to delete that code
and replace it with wiggle-based stuff real soon.

crates/wasi-common/wig/src/hostcalls.rs

@@ -96,7 +96,7 @@ fn generate_wrappers(func: &witx::InterfaceFunc, old: bool) -> TokenStream {
             let ret = #call
                 .err()
                 .unwrap_or(super::wasi::WasiError::ESUCCESS);
-            log::trace!("     | errno={}", ret);
+            tracing::trace!("     | errno={}", ret);
             ret.as_raw_errno()
         }
     };