extension: Make worktree argument to run_slash_command optional (#15658)

This PR updates the extension API to make the `worktree` argument to
`run_slash_command` optional.

We may not always have a worktree, and not all slash commands need them,
so by making it optional we can allow individual slash commands to
decide what to do when there is no worktree.

Release Notes:

- N/A

crates/extension/src/wasm_host/wit.rs

@@ -277,7 +277,7 @@ impl Extension {
         store: &mut Store<WasmState>,
         command: &SlashCommand,
         argument: Option<&str>,
-        resource: Resource<Arc<dyn LspAdapterDelegate>>,
+        resource: Option<Resource<Arc<dyn LspAdapterDelegate>>>,
     ) -> Result<Result<SlashCommandOutput, String>> {
         match self {
             Extension::V007(ext) => {