Migrate from winapi to windows-sys (#4346)

* Migrate from `winapi` to `windows-sys`

I believe that Microsoft itself is supporting the development of
`windows-sys` and it's also used by `cap-std` now so this switches
Wasmtime's dependencies on Windows APIs from the `winapi` crate to the
`windows-sys` crate. We still have `winapi` in our dependency graph but
that may get phased out over time.

* Make windows-sys a target-specific dependency

Cargo.toml

@@ -55,13 +55,15 @@ tracing-subscriber = "0.3.1"
 wast = "42.0.0"
 criterion = "0.3.4"
 num_cpus = "1.13.0"
-winapi = { version = "0.3.9", features = ['memoryapi'] }
 memchr = "2.4"
 async-trait = "0.1"
 wat = "1.0.43"
 once_cell = "1.9.0"
 rayon = "1.5.0"
 
+[target.'cfg(windows)'.dev-dependencies]
+windows-sys = { version = "0.36.0", features = ["Win32_System_Memory"] }
+
 [build-dependencies]
 anyhow = "1.0.19"