[wasi-common]: yanix now returns io::Error directly (#1242)

* Yanix now returns io::Error

This commit may seem somewhat controversial at first, but hear me
out first. Currently, Yanix would return a custom error that's a
wrapper around three other error types returned by various entities
inside Rust's `libstd`. In particular, Yanix's error type would wrap
`io::Error`, `num::TryFromIntError` and `ffi::NulError`. It turns
out that there is a natural conversion between the first and the last
and provided by the standard library, i.e., `From<ffi::NulError> for io::Error`
is provided. So at the surface it may seem that only the first two
wrapped error types are worth keeping.

Digging a little bit deeper into `libstd`, `num::TryFromIntError`
is essentially speaking only a marker that the integral conversion
went wrong. The struct implementing this error stores a unit type,
and nothing more. It therefore seems like a waste to wrap this
particular error when we could unify everything under `io::Error`.
And so, whenever we perform an int conversion, I suggest we simply
remap the error to `io::Error::from_raw_os_error(libc::EOVERFLOW)`
since this carries a comparable amount of information.

As a result of completely discarding `yanix::Error` custom error type,
we are invariably simplifying `yanix` itself, but also allowing
`wasi-common` to simplify in several places as well.

* Adapt wasi-common to changes in yanix

* Add Cargo.lock

* Unwrap try_into's where possible

* Remove unnecessary type annotation

Cargo.lock

@@ -2607,7 +2607,6 @@ dependencies = [
  "cfg-if",
  "libc",
  "log",
- "thiserror",
 ]
 
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