Add commands to select next/previous siblings in the syntax tree (#35053)

Closes #5133 and discussion
https://github.com/zed-industries/zed/discussions/33493

This PR adds two new commands to select next/previous siblings in the
syntax tree. These commands were modelled after the existing ones about
expand/shrink selection. With this PR I've added new key bindings
inspired by `helix` for previous / next / expand / shrink selections.



https://github.com/user-attachments/assets/4ef7fadb-0b82-4897-95c7-1737827bf4ac


Release Notes:

- Add commands to select next/previous siblings in the syntax tree

---------

Co-authored-by: Joseph T. Lyons <JosephTLyons@gmail.com>

crates/zed/src/zed/app_menus.rs

@@ -127,6 +127,11 @@ pub fn app_menus() -> Vec<Menu> {
                 ),
                 MenuItem::action("Expand Selection", editor::actions::SelectLargerSyntaxNode),
                 MenuItem::action("Shrink Selection", editor::actions::SelectSmallerSyntaxNode),
+                MenuItem::action("Select Next Sibling", editor::actions::SelectNextSyntaxNode),
+                MenuItem::action(
+                    "Select Previous Sibling",
+                    editor::actions::SelectPreviousSyntaxNode,
+                ),
                 MenuItem::separator(),
                 MenuItem::action("Add Cursor Above", editor::actions::AddSelectionAbove),
                 MenuItem::action("Add Cursor Below", editor::actions::AddSelectionBelow),