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/slash_command/now_command.rs

@@ -7,7 +7,7 @@ use assistant_slash_command::{
 };
 use chrono::Local;
 use gpui::{Task, WeakView};
-use language::LspAdapterDelegate;
+use language::{BufferSnapshot, LspAdapterDelegate};
 use ui::prelude::*;
 use workspace::Workspace;
 
@@ -43,6 +43,8 @@ impl SlashCommand for NowSlashCommand {
     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,
@@ -57,6 +59,7 @@ impl SlashCommand for NowSlashCommand {
                 range,
                 icon: IconName::CountdownTimer,
                 label: now.to_rfc2822().into(),
+                metadata: None,
             }],
             run_commands_in_text: false,
         }))