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/extension_slash_command.rs

@@ -91,10 +91,11 @@ impl SlashCommand for ExtensionSlashCommand {
                     let this = self.clone();
                     move |extension, store| {
                         async move {
-                            let delegate = delegate.ok_or_else(|| {
-                                anyhow!("no worktree for extension slash command")
-                            })?;
-                            let resource = store.data_mut().table().push(delegate)?;
+                            let resource = if let Some(delegate) = delegate {
+                                Some(store.data_mut().table().push(delegate)?)
+                            } else {
+                                None
+                            };
                             let output = extension
                                 .call_run_slash_command(
                                     store,

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) => {