[wasi-common] Log string representation of WASI errno at the trace level (#760)

* Log str repr of WASI errno at trace level

This commit refactors `Error` enum, and adds logging of the WASI
errno string representation at the trace level. Now, when tracing
WASI syscalls, we will be greeted with a nicely formatted errno
value after each syscall:

```
path_open(...)
     | *fd=5
     | errno=ESUCCESS
```

This commit gets rid of `errno_from_nix`, `errno_from_win` and
`errno_from_host` helper fns in favour of direct `From` implementations
for the relevant types such as `yanix::Errno` and `winx::winerror::WinError`.
`errno_from_host` is replaced by a trait `FromRawOsError`.

* Back port changes to snapshot0

* Fix indentation in logs

crates/wasi-common/src/hostcalls_impl/misc.rs

@@ -261,7 +261,7 @@ pub(crate) fn poll_oneoff(
                         let event = wasi::__wasi_event_t {
                             userdata: subscription.userdata,
                             r#type,
-                            error: err.as_wasi_errno(),
+                            error: err.as_wasi_error().as_raw_errno(),
                             u: wasi::__wasi_event_u_t {
                                 fd_readwrite: wasi::__wasi_event_fd_readwrite_t {
                                     nbytes: 0,