Add support for detecting tests in source files, and implement it for Rust (#11195)

Continuing work from #10873 

Release Notes:

- N/A

---------

Co-authored-by: Mikayla <mikayla@zed.dev>

crates/editor/src/mouse_context_menu.rs

@@ -79,7 +79,7 @@ pub fn deploy_context_menu(
                 .action(
                     "Code Actions",
                     Box::new(ToggleCodeActions {
-                        deployed_from_indicator: false,
+                        deployed_from_indicator: None,
                     }),
                 )
                 .separator()