This commit renames `wasi_config_set_std[in|out|err]` to
`wasi_config_set_std[in|out|err]_file` so we can reserve the former for
when the C API supports a stream abstraction.
This commit implements an initial WASI C API that can be used to instantiate
and configure a WASI instance from C.
This also implements a `WasiBuilder` for the C# API enabling .NET hosts to bind
to Wasmtime's WASI implementation.
It appears there are two trailing null bytes at the end of the string.
This does not seem right. But it might be a good idea generally to remove
any null bytes that get into error messages.
For Windows release builds, the `wasm_valtype_kind` C API return value
is being returned as a single byte.
The .NET interop signature for this function was expecting an
integer-sized return, resulting in three extra bytes being used on
Windows.
The fix is to limit the corresponding C# enum to a byte representation,
which will properly mask the return value from `wasm_valtype_kind`.
CI has also been updated to test both debug and release configurations
(previously it was only testing debug, hence why this was missed).
Also fixed a cast bug in the `declare_vec!` macro in the C API when the
element types were pointers to values. The `as_slice` implementation
was incorrectly casting away a level of pointer indirection, resulting
in corrupted data when accessing the slice's elements.
