[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/mod.rs

@@ -1,4 +1,3 @@
-use crate::wasi;
 use cfg_if::cfg_if;
 
 cfg_if! {
@@ -6,18 +5,10 @@ cfg_if! {
         mod unix;
         pub(crate) use unix::*;
         pub use unix::preopen_dir;
-
-        pub(crate) fn errno_from_host(err: i32) -> wasi::__wasi_errno_t {
-            host_impl::errno_from_nix(yanix::Errno::from_i32(err)).as_wasi_errno()
-        }
     } else if #[cfg(windows)] {
         mod windows;
         pub(crate) use windows::*;
         pub use windows::preopen_dir;
-
-        pub(crate) fn errno_from_host(err: i32) -> wasi::__wasi_errno_t {
-            host_impl::errno_from_win(winx::winerror::WinError::from_u32(err as u32))
-        }
     } else {
         compile_error!("wasi-common doesn't compile for this platform yet");
     }