Introduce a new /delta command (#17903)

Release Notes:

- Added a new `/delta` command to re-insert changed files that were
previously included in a context.

---------

Co-authored-by: Roy <roy@anthropic.com>

crates/assistant/src/context/context_tests.rs

@@ -12,7 +12,7 @@ use assistant_slash_command::{
 use collections::HashSet;
 use fs::FakeFs;
 use gpui::{AppContext, Model, SharedString, Task, TestAppContext, WeakView};
-use language::{Buffer, LanguageRegistry, LspAdapterDelegate};
+use language::{Buffer, BufferSnapshot, LanguageRegistry, LspAdapterDelegate};
 use language_model::{LanguageModelCacheConfiguration, LanguageModelRegistry, Role};
 use parking_lot::Mutex;
 use project::Project;
@@ -1089,6 +1089,7 @@ async fn test_random_context_collaboration(cx: &mut TestAppContext, mut rng: Std
                             range: section_start..section_end,
                             icon: ui::IconName::Ai,
                             label: "section".into(),
+                            metadata: None,
                         });
                     }
 
@@ -1425,6 +1426,8 @@ impl SlashCommand for FakeSlashCommand {
     fn run(
         self: Arc<Self>,
         _arguments: &[String],
+        _context_slash_command_output_sections: &[SlashCommandOutputSection<language::Anchor>],
+        _context_buffer: BufferSnapshot,
         _workspace: WeakView<Workspace>,
         _delegate: Option<Arc<dyn LspAdapterDelegate>>,
         _cx: &mut WindowContext,