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/test-helpers/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "component-macro-test-helpers"
+version = "0.0.0"
+edition.workspace = true
+publish = false
+license = "Apache-2.0 WITH LLVM-exception"
+
+[lib]
+proc-macro = true
+
+[dependencies]
+proc-macro2 = "1.0"
+quote = "1.0"

crates/component-macro/test-helpers/src/lib.rs

@@ -0,0 +1,23 @@
+use proc_macro::TokenStream;
+use proc_macro2::{Ident, Span};
+use quote::quote;
+
+#[proc_macro]
+pub fn foreach(input: TokenStream) -> TokenStream {
+    let input = proc_macro2::TokenStream::from(input);
+    let mut cwd = std::env::current_dir().unwrap();
+    cwd.push("crates/component-macro/tests/codegen");
+    let mut result = Vec::new();
+    for f in cwd.read_dir().unwrap() {
+        let f = f.unwrap().path();
+        if f.extension().and_then(|s| s.to_str()) == Some("wit") {
+            let name = f.file_stem().unwrap().to_str().unwrap();
+            let name = Ident::new(&name.replace("-", "_"), Span::call_site());
+            let path = f.to_str().unwrap();
+            result.push(quote! {
+                #input!(#name #path);
+            });
+        }
+    }
+    (quote!( #(#result)*)).into()
+}