This changes the minimum terminal dimensions from 2 lines and 2 columns,
to 1 line and 2 columns.
This also reworks the `SizeInfo` to store the number of columns and
lines and consistently has only the terminal lines/columns stored,
instead of including the message bar and search in some places of the
Alacritty renderer/input.
These new changes also make it easy to properly start the selection
scrolling as soon as the mouse is over the message bar, instead of
waiting until it is beyond it.
Fixes#4207.
Co-authored-by: Christian Duerr <contact@christianduerr.com>