Return DELTA if WINDOW can be resized vertically by DELTA lines.
WINDOW must be a valid window and defaults to the selected one.
Optional argument HORIZONTAL non-nil means return DELTA if WINDOW
can be resized horizontally by DELTA columns. A return value of
zero means that WINDOW is not resizable.
DELTA positive means WINDOW shall be enlarged by DELTA lines or
columns. If WINDOW cannot be enlarged by DELTA lines or columns
return the maximum value in the range 0..DELTA by which WINDOW
can be enlarged.
DELTA negative means WINDOW shall be shrunk by -DELTA lines or
columns. If WINDOW cannot be shrunk by -DELTA lines or columns,
return the minimum value in the range DELTA..0 that can be used
for shrinking WINDOW.
Optional argument IGNORE non-nil means ignore restrictions
imposed by fixed size windows, `window-min-height' or
`window-min-width' settings. If IGNORE is a window, ignore
restrictions for that window only. If IGNORE equals `safe',
live windows may get as small as `window-safe-min-height' lines
and `window-safe-min-width' columns. Any other non-nil value
means ignore all of the above restrictions for all windows.