Change default pane split directions (#36101)

Closes #32538

This PR adjusts the defaults for splitting panes along the horizontal
and vertical actions. Based upon user feedback, the adjusted values seem
more reasonable as default settings, hence, go with these instead.

Release Notes:

- Changed the default split directions for the `pane: split horizontal`
and `pane: split vertical` actions. You can restore the old behavior by
modifying the `pane_split_direction_horizontal` and
`pane_split_direction_vertical` values in your settings.

assets/settings/default.json

@@ -82,10 +82,10 @@
   // Layout mode of the bottom dock. Defaults to "contained"
   //   choices: contained, full, left_aligned, right_aligned
   "bottom_dock_layout": "contained",
-  // The direction that you want to split panes horizontally. Defaults to "up"
-  "pane_split_direction_horizontal": "up",
-  // The direction that you want to split panes vertically. Defaults to "left"
-  "pane_split_direction_vertical": "left",
+  // The direction that you want to split panes horizontally. Defaults to "down"
+  "pane_split_direction_horizontal": "down",
+  // The direction that you want to split panes vertically. Defaults to "right"
+  "pane_split_direction_vertical": "right",
   // Centered layout related settings.
   "centered_layout": {
     // The relative width of the left padding of the central pane from the