Add arrow key mappings for tree-sitter parent/child/sibling nav (#1724)

* 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.

* Add new bindings to docs

book/src/keymap.md

@@ -119,10 +119,10 @@
 | `K`                  | Keep selections matching the regex                                | `keep_selections`                    |
 | `Alt-K`              | Remove selections matching the regex                              | `remove_selections`                  |
 | `Ctrl-c`             | Comment/uncomment the selections                                  | `toggle_comments`                    |
-| `Alt-k`  | Expand selection to parent syntax node (**TS**)                   | `expand_selection`                   |
+| `Alt-k`/`Alt-up`     | Expand selection to parent syntax node (**TS**)                   | `expand_selection`                   |
-| `Alt-j`  | Shrink syntax tree object selection (**TS**)                      | `shrink_selection`                   |
+| `Alt-j`/`Alt-down`   | Shrink syntax tree object selection (**TS**)                      | `shrink_selection`                   |
-| `Alt-h`  | Select previous sibling node in syntax tree (**TS**)              | `select_prev_sibling`                |
+| `Alt-h`/`Alt-left`   | Select previous sibling node in syntax tree (**TS**)              | `select_prev_sibling`                |
-| `Alt-l`  | Select next sibling node in syntax tree (**TS**)                  | `select_next_sibling`                |
+| `Alt-l`/`Alt-right`  | Select next sibling node in syntax tree (**TS**)                  | `select_next_sibling`                |
 
 ### Search
 

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-k" | "A-up" => expand_selection,
-            "A-j" => shrink_selection,
+            "A-j" | "A-down" => shrink_selection,
-            "A-h" => select_prev_sibling,
+            "A-h" | "A-left" => select_prev_sibling,
-            "A-l" => select_next_sibling,
+            "A-l" | "A-right" => select_next_sibling,
 
             "%" => select_all,
             "x" => extend_line,