Add a picker for jj bookmark list (#30883)

This PR adds a new picker for viewing a list of jj bookmarks, like you
would with `jj bookmark list`.

This is an exploration around what it would look like to begin adding
some dedicated jj features to Zed.

This is behind the `jj-ui` feature flag.

Release Notes:

- N/A

crates/jj/src/jj_store.rs

@@ -0,0 +1,41 @@
+use std::path::Path;
+use std::sync::Arc;
+
+use gpui::{App, Entity, Global, prelude::*};
+
+use crate::{JujutsuRepository, RealJujutsuRepository};
+
+/// Note: We won't ultimately be storing the jj store in a global, we're just doing this for exploration purposes.
+struct GlobalJujutsuStore(Entity<JujutsuStore>);
+
+impl Global for GlobalJujutsuStore {}
+
+pub struct JujutsuStore {
+    repository: Arc<dyn JujutsuRepository>,
+}
+
+impl JujutsuStore {
+    pub fn init_global(cx: &mut App) {
+        let Some(repository) = RealJujutsuRepository::new(&Path::new(".")).ok() else {
+            return;
+        };
+
+        let repository = Arc::new(repository);
+        let jj_store = cx.new(|cx| JujutsuStore::new(repository, cx));
+
+        cx.set_global(GlobalJujutsuStore(jj_store));
+    }
+
+    pub fn try_global(cx: &App) -> Option<Entity<Self>> {
+        cx.try_global::<GlobalJujutsuStore>()
+            .map(|global| global.0.clone())
+    }
+
+    pub fn new(repository: Arc<dyn JujutsuRepository>, _cx: &mut Context<Self>) -> Self {
+        Self { repository }
+    }
+
+    pub fn repository(&self) -> &Arc<dyn JujutsuRepository> {
+        &self.repository
+    }
+}