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/records.wit

@@ -0,0 +1,60 @@
+interface records {
+  tuple-arg: func(x: tuple<char, u32>)
+  tuple-result: func() -> tuple<char, u32>
+
+  record empty {}
+
+  empty-arg: func(x: empty)
+  empty-result: func() -> empty
+
+  /// A record containing two scalar fields
+  /// that both have the same type
+  record scalars {
+      /// The first field, named a
+      a: u32,
+      /// The second field, named b
+      b: u32,
+  }
+
+  scalar-arg: func(x: scalars)
+  scalar-result: func() -> scalars
+
+  /// A record that is really just flags
+  /// All of the fields are bool
+  record really-flags {
+      a: bool,
+      b: bool,
+      c: bool,
+      d: bool,
+      e: bool,
+      f: bool,
+      g: bool,
+      h: bool,
+      i: bool,
+  }
+
+  flags-arg: func(x: really-flags)
+  flags-result: func() -> really-flags
+
+  record aggregates {
+      a: scalars,
+      b: u32,
+      c: empty,
+      d: string,
+      e: really-flags,
+  }
+
+  aggregate-arg: func(x: aggregates)
+  aggregate-result: func() -> aggregates
+
+  type tuple-typedef = tuple<s32>
+  type int-typedef = s32
+  type tuple-typedef2 = tuple<int-typedef>
+  typedef-inout: func(e: tuple-typedef2) -> s32
+}
+
+world the-world {
+  import imports: records
+  export exports: records
+  default export records
+}