Decouple extension Worktree resource from LspAdapterDelegate (#20611)

This PR decouples the extension `Worktree` resource from the
`LspAdapterDelegate`.

We now have a `WorktreeDelegate` trait that corresponds to the methods
on the resource.

We then create a `WorktreeDelegateAdapter` that can wrap an
`LspAdapterDelegate` and implement the `WorktreeDelegate` trait.

Release Notes:

- N/A

crates/extensions_ui/src/extension_slash_command.rs

@@ -5,6 +5,7 @@ use assistant_slash_command::{
     ArgumentCompletion, SlashCommand, SlashCommandOutput, SlashCommandOutputSection,
     SlashCommandResult,
 };
+use extension_host::extension_lsp_adapter::WorktreeDelegateAdapter;
 use futures::FutureExt as _;
 use gpui::{Task, WeakView, WindowContext};
 use language::{BufferSnapshot, LspAdapterDelegate};
@@ -97,6 +98,8 @@ impl SlashCommand for ExtensionSlashCommand {
                     move |extension, store| {
                         async move {
                             let resource = if let Some(delegate) = delegate {
+                                let delegate =
+                                    Arc::new(WorktreeDelegateAdapter(delegate.clone())) as _;
                                 Some(store.data_mut().table().push(delegate)?)
                             } else {
                                 None