Prefer to disable options over hiding (git panel entry context menu) (#44102)

When adding the File History option here, I used the pattern to hide the
option, since that's what another option was already doing here, but I
see other menus in the git panel (`...`) that use disabling over hiding,
which is what I think is a nicer experience (allows you to learn of
actions, the full range of actions is always visible, don't have to
worry about how multiple hidden items might interact in various
configurations, etc).

<img width="336" height="241" alt="SCR-20251203-pnpy"
src="https://github.com/user-attachments/assets/0da90b9a-c230-4ce3-87b9-553ffb83604f"
/>

<img width="332" height="265" alt="SCR-20251203-pobg"
src="https://github.com/user-attachments/assets/5da95c7d-faa9-4f0f-a069-f1d099f952b9"
/>


In general, I think it would be good to move to being more consistent
with disabling over hiding - there are other places in the app that are
hiding - some might be valid, but others might just choices made on a
whim.

Release Notes:

- N/A

crates/git_ui/src/git_panel.rs

@@ -4004,28 +4004,21 @@ impl GitPanel {
             "Restore File"
         };
         let context_menu = ContextMenu::build(window, cx, |context_menu, _, _| {
-            let mut context_menu = context_menu
+            let is_created = entry.status.is_created();
+            context_menu
                 .context(self.focus_handle.clone())
                 .action(stage_title, ToggleStaged.boxed_clone())
-                .action(restore_title, git::RestoreFile::default().boxed_clone());
-
-            if entry.status.is_created() {
-                context_menu =
-                    context_menu.action("Add to .gitignore", git::AddToGitignore.boxed_clone())
-            }
-
-            context_menu = context_menu
+                .action(restore_title, git::RestoreFile::default().boxed_clone())
+                .action_disabled_when(
+                    !is_created,
+                    "Add to .gitignore",
+                    git::AddToGitignore.boxed_clone(),
+                )
                 .separator()
                 .action("Open Diff", Confirm.boxed_clone())
-                .action("Open File", SecondaryConfirm.boxed_clone());
-
-            if !entry.status.is_created() {
-                context_menu = context_menu
-                    .separator()
-                    .action("File History", Box::new(git::FileHistory));
-            }
-
-            context_menu
+                .action("Open File", SecondaryConfirm.boxed_clone())
+                .separator()
+                .action_disabled_when(is_created, "File History", Box::new(git::FileHistory))
         });
         self.selected_entry = Some(ix);
         self.set_context_menu(context_menu, position, window, cx);