Add a wasmtime::component::bindgen! macro (#5317)

* Import Wasmtime support from the `wit-bindgen` repo

This commit imports the `wit-bindgen-gen-host-wasmtime-rust` crate from
the `wit-bindgen` repository into the upstream Wasmtime repository. I've
chosen to not import the full history here since the crate is relatively
small and doesn't have a ton of complexity. While the history of the
crate is quite long the current iteration of the crate's history is
relatively short so there's not a ton of import there anyway. The
thinking is that this can now continue to evolve in-tree.

* Refactor `wasmtime-component-macro` a bit

Make room for a `wit_bindgen` macro to slot in.

* Add initial support for a `bindgen` macro

* Add tests for `wasmtime::component::bindgen!`

* Improve error forgetting `async` feature

* Add end-to-end tests for bindgen

* Add an audit of `unicase`

* Add a license to the test-helpers crate

* Add vet entry for `pulldown-cmark`

* Update publish script with new crate

* Try to fix publish script

* Update audits

* Update lock file

crates/component-macro/tests/codegen.rs

@@ -0,0 +1,24 @@
+macro_rules! gentest {
+    ($id:ident $path:tt) => {
+        mod $id {
+            mod normal {
+                wasmtime::component::bindgen!($path);
+            }
+            mod async_ {
+                wasmtime::component::bindgen!({
+                    path: $path,
+                    async: true,
+                });
+            }
+            mod tracing {
+                wasmtime::component::bindgen!({
+                    path: $path,
+                    tracing: true,
+                });
+            }
+        }
+        // ...
+    };
+}
+
+component_macro_test_helpers::foreach!(gentest);