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

supply-chain/config.toml

@@ -338,10 +338,6 @@ criteria = "safe-to-deploy"
 version = "0.10.0"
 criteria = "safe-to-deploy"
 
-[[exemptions.half]]
-version = "1.8.2"
-criteria = "safe-to-run"
-
 [[exemptions.hermit-abi]]
 version = "0.1.19"
 criteria = "safe-to-deploy"
@@ -738,10 +734,6 @@ criteria = "safe-to-deploy"
 version = "1.0.137"
 criteria = "safe-to-deploy"
 
-[[exemptions.serde_cbor]]
-version = "0.11.2"
-criteria = "safe-to-run"
-
 [[exemptions.serde_derive]]
 version = "1.0.137"
 criteria = "safe-to-deploy"