Add arrow key mappings for tree-sitter parent/child/sibling nav

This helps my use case, where I use a non-qwerty layout with a
programmable mechanical keyboard, and use a layer switching key (think
fn) to send left down up right from the traditional hjkl positions.

helix-term/src/keymap.rs

@@ -584,10 +584,10 @@ impl Default for Keymaps {
             "S" => split_selection,
             ";" => collapse_selection,
             "A-;" => flip_selections,
-            "A-k" => expand_selection,
-            "A-j" => shrink_selection,
-            "A-h" => select_prev_sibling,
-            "A-l" => select_next_sibling,
+            "A-k" | "A-up" => expand_selection,
+            "A-j" | "A-down" => shrink_selection,
+            "A-h" | "A-left" => select_prev_sibling,
+            "A-l" | "A-right" => select_next_sibling,
 
             "%" => select_all,
             "x" => extend_line,