Returns a lua representation of the
that identifies the dimensions and position of the viewport as
well as the scrollback for the pane.
It has the following fields:
colsthe number of columns
viewport_rowsthe number of vertical cells in the visible portion of the window
scrollback_rowsthe total number of lines in the scrollback and viewport
physical_topthe top of the physical non-scrollback screen expressed as a stable index.
scrollback_topthe top of the scrollback; the earliest row remembered by wezterm.