extension: Upgrade wasmtime to v21 (#15210)

This PR upgrades the version of `wasmtime` and `wasmtime-wasi` in use to
v21.0.1.

We have to skip v20 because Tree-sitter also skipped it.

Here are the changes that had to be made:

### v19 -> v20

After upgrading the `wasmtime` packages to v20, I also had to run `cargo
update -p mach2` to pull in
[v0.4.2](https://github.com/JohnTitor/mach2/releases/tag/0.4.2) to fix
some compile errors.

There were a few minor API changes in `wasmtime-wasi` from
https://github.com/bytecodealliance/wasmtime/pull/8228 that we needed to
account for.

### v20 -> v21

Since there isn't a Tree-sitter version that depends on `wasmtime@v20`,
we're jumping straight to v21.

The published version of Tree-sitter (v0.22.6) still depends on
`wasmtime@v19`, but there was a commit
(7f4a57817d)
later that month that upgrades the `wasmtime` dependency to v21.

We're patching Tree-sitter to that commit so we can get the new
`wasmtime` version.

The main change in v21 is that imports generated by `bindgen!` are no
longer automatically trapped
(https://github.com/bytecodealliance/wasmtime/pull/8310), so we need to
add `trappable_imports: true` to our `bindgen!` calls.

Release Notes:

- N/A

crates/extension/src/wasm_host/wit.rs

@@ -29,7 +29,7 @@ pub fn new_linker(
     f: impl Fn(&mut Linker<WasmState>, fn(&mut WasmState) -> &mut WasmState) -> Result<()>,
 ) -> Linker<WasmState> {
     let mut linker = Linker::new(&wasm_engine());
-    wasmtime_wasi::command::add_to_linker(&mut linker).unwrap();
+    wasmtime_wasi::add_to_linker_async(&mut linker).unwrap();
     f(&mut linker, wasi_view).unwrap();
     linker
 }