assistant2: Suggest current file as context (#22526)

Suggest adding the current file as context in the new assistant panel.



https://github.com/user-attachments/assets/62bc267b-3dfe-4a3b-a6af-c89af2c779a8


Note: This doesn't include suggesting the current thread in the inline
assistant.

Release Notes:

- N/A

crates/assistant2/src/context_store.rs

@@ -1,4 +1,5 @@
 use gpui::SharedString;
+use project::ProjectEntryId;
 
 use crate::context::{Context, ContextId, ContextKind};
 
@@ -44,4 +45,13 @@ impl ContextStore {
     pub fn remove_context(&mut self, id: &ContextId) {
         self.context.retain(|context| context.id != *id);
     }
+
+    pub fn contains_project_entry(&self, entry_id: ProjectEntryId) -> bool {
+        self.context.iter().any(|probe| match probe.kind {
+            ContextKind::File(probe_entry_id) => probe_entry_id == entry_id,
+            ContextKind::Directory => false,
+            ContextKind::FetchedUrl => false,
+            ContextKind::Thread => false,
+        })
+    }
 }