[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/sys/unix/hostcalls_impl/misc.rs

@@ -1,7 +1,6 @@
 #![allow(non_camel_case_types)]
 #![allow(unused_unsafe)]
 use crate::hostcalls_impl::{ClockEventData, FdEventData};
-use crate::sys::host_impl;
 use crate::{wasi, Error, Result};
 use yanix::clock::{clock_getres, clock_gettime, ClockId};
 
@@ -92,7 +91,7 @@ pub(crate) fn poll_oneoff(
                 if Errno::last() == Errno::EINTR {
                     continue;
                 }
-                return Err(host_impl::errno_from_nix(Errno::last()));
+                return Err(Errno::last().into());
             }
             Ok(ready) => break ready,
         }