cmd_split: fix toggle split for non-split layouts
cmd_split: fix toggle split for non-split layouts

Previously, `layout toggle` and `layout toggle split` would set L_VERT
when layout was L_HORIZ, otherwise it would set L_HORIZ. This meant
that when the layout was L_TABBED or L_STACKED, it would always be
L_HORIZ. This extends #4315 (which corrects the handling when multiple
layouts are given) to try prev_split_layout,
config->default_orientation, and then falling back to L_VERT when the
output is taller than wide and L_HORIZ when wider than tall.

ascent12/sway,SirCmpwn/sway,1ace/sway,ascent12/sway,ascent12/sway,1ace/sway,1ace/sway