refactor: rename open_changed_files to show_vcs_status

This fits a bit better as we will add commands to do more than just
open the files in the status palette.

src/keybind/builtin/helix.json

@@ -228,7 +228,7 @@
             ["space R", "replace_selections_with_clipboard"],
             ["space ?", "open_command_palette"],
             ["space f", "find_file"],
-            ["space g", "open_changed_files"],
+            ["space g", "show_vcs_status"],
             ["space b", "switch_buffers"],
             ["space j", "jumplist_picker"],
             ["space s", "symbol_picker"],