Add wasix_http_client Rust client library

Adds a new crate "wasix_http_client", which is a wrapper around the WAI
generated sys bindings to the wasix_http_client_v1.wai component.

Enables easy http client usage from Rust code.

lib/wasix/wasix-http-client/examples/http_client.rs

@@ -0,0 +1,20 @@
+use wasix_http_client::{Body, HttpClient, RequestBuilder};
+
+fn main() {
+    let c = HttpClient::new().unwrap();
+    let r = RequestBuilder::new()
+        .uri("http://ferris2.christoph.app.wapm.dev/http-client-test")
+        .body(Body::empty())
+        .unwrap();
+    eprintln!("fetching: {r:?}");
+
+    let res = c.send(r).unwrap();
+    dbg!(&res);
+    assert!(res.status().is_success());
+
+    let body = res.into_body().read_all().unwrap();
+    let s = String::from_utf8(body).unwrap();
+    eprintln!("Response body: {s}");
+
+    assert!(s.contains("http-client-test"));
+}