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

tests/all/component_model/bindgen.rs

@@ -0,0 +1,117 @@
+use super::engine;
+use anyhow::Result;
+use wasmtime::{
+    component::{Component, Linker},
+    Store,
+};
+
+mod no_imports {
+    use super::*;
+
+    wasmtime::component::bindgen!({
+        inline: "
+            world no-imports {
+                export foo: interface {
+                    foo: func()
+                }
+
+                default export interface {
+                    bar: func()
+                }
+            }
+        ",
+    });
+
+    #[test]
+    fn run() -> Result<()> {
+        let engine = engine();
+
+        let component = Component::new(
+            &engine,
+            r#"
+                (component
+                    (core module $m
+                        (func (export ""))
+                    )
+                    (core instance $i (instantiate $m))
+
+                    (func $f (export "bar") (canon lift (core func $i "")))
+
+                    (instance $i (export "foo" (func $f)))
+                    (export "foo" (instance $i))
+                )
+            "#,
+        )?;
+
+        let linker = Linker::new(&engine);
+        let mut store = Store::new(&engine, ());
+        let (no_imports, _) = NoImports::instantiate(&mut store, &component, &linker)?;
+        no_imports.bar(&mut store)?;
+        no_imports.foo().foo(&mut store)?;
+        Ok(())
+    }
+}
+
+mod one_import {
+    use super::*;
+
+    wasmtime::component::bindgen!({
+        inline: "
+            world one-import {
+                import foo: interface {
+                    foo: func()
+                }
+
+                default export interface {
+                    bar: func()
+                }
+            }
+        ",
+    });
+
+    #[test]
+    fn run() -> Result<()> {
+        let engine = engine();
+
+        let component = Component::new(
+            &engine,
+            r#"
+                (component
+                    (import "foo" (instance $i
+                        (export "foo" (func))
+                    ))
+                    (core module $m
+                        (import "" "" (func))
+                        (export "" (func 0))
+                    )
+                    (core func $f (canon lower (func $i "foo")))
+                    (core instance $i (instantiate $m
+                        (with "" (instance (export "" (func $f))))
+                    ))
+
+                    (func $f (export "bar") (canon lift (core func $i "")))
+                )
+            "#,
+        )?;
+
+        #[derive(Default)]
+        struct MyImports {
+            hit: bool,
+        }
+
+        impl foo::Foo for MyImports {
+            fn foo(&mut self) -> Result<()> {
+                self.hit = true;
+                Ok(())
+            }
+        }
+
+        let mut linker = Linker::new(&engine);
+        foo::add_to_linker(&mut linker, |f: &mut MyImports| f)?;
+        let mut store = Store::new(&engine, MyImports::default());
+        let (one_import, _) = OneImport::instantiate(&mut store, &component, &linker)?;
+        one_import.bar(&mut store)?;
+        assert!(store.data().hit);
+        Ok(())
+    }
+}