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.

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

crates/assistant/src/slash_command.rs

@@ -22,6 +22,7 @@ use workspace::Workspace;
 pub mod auto_command;
 pub mod context_server_command;
 pub mod default_command;
+pub mod delta_command;
 pub mod diagnostics_command;
 pub mod docs_command;
 pub mod fetch_command;