x64: enable VTune support by default (#3821)

* x64: enable VTune support by default

After significant work in the `ittapi-rs` crate, this dependency should
build without issue on Wasmtime's supported operating systems: Windows,
Linux, and macOS. The difference in the release binary is <20KB, so this
change makes `vtune` a default build feature. This change upgrades
`ittapi-rs` to v0.2.0 and updates the documentation.

* review: add configuration for defaults in more places

* review: remove OS conditional compilation, add architecture

* review: do not default vtune feature in wasmtime-jit

Cargo.lock

@@ -1497,9 +1497,9 @@ checksum = "1aab8fc367588b89dcee83ab0fd66b72b50b72fa1904d7095045ace2b0c81c35"
 
 [[package]]
 name = "ittapi-rs"
-version = "0.1.6"
+version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "265ed25cd5b53e9b02bf97a1f66ab7af1af7ab61f5d9ce1e05aeaed098723658"
+checksum = "f712648a1ad72fbfb7adc2772c331e8d90f022f8cf30cbabefba2878dd3172b0"
 dependencies = [
  "cc",
 ]