Return non-nil if `split-window-sensibly' may split WINDOW.
Optional argument HORIZONTAL nil or omitted means check whether
`split-window-sensibly' may split WINDOW vertically. HORIZONTAL
non-nil means check whether WINDOW may be split horizontally.
WINDOW may be split vertically when the following conditions
hold:
- `window-size-fixed' is either nil or equals `width' for the
buffer of WINDOW.
- `split-height-threshold' is an integer and WINDOW is at least as
high as `split-height-threshold'.
- When WINDOW is split evenly, the emanating windows are at least
`window-min-height' lines tall and can accommodate at least one
line plus - if WINDOW has one - a mode line.
WINDOW may be split horizontally when the following conditions
hold:
- `window-size-fixed' is either nil or equals `height' for the
buffer of WINDOW.
- `split-width-threshold' is an integer and WINDOW is at least as
wide as `split-width-threshold'.
- When WINDOW is split evenly, the emanating windows are at least
`window-min-width' or two (whichever is larger) columns wide.