Problem: Traditionally, the ruler in the last line is one cell shorter
than in the statusline, leaving the last cell of the screen blank.
According to code comments, this is in order to prevent unwanted
scrolling on "some" (unspecified, but presumably ancient) terminals.
Berkeley vi is more specific in its `vs_modeline` function: dumb
terminals with hardware scroll, SunOS 4.1.1 and Ultrix 4.2 curses.
(n)curses still has a similar limitation in `(w)addstr`, but apparently
only for historical reasons.
Maintaining the different widths leads to awkward inconsistencies when
the ruler is configured with 'rulerformat', except for the special case
where it contains a top-level `%=`. Shifting the ruler in the last line
to the left would be a solution, but the empty cell at the end doesn't
seem to be relevant anymore.
Solution: extend the ruler in the last line all the way to the right
edge of the screen, just like in the statusline. The exact same amount
of place will be available to the rest of the UI as before.
BREAKING CHANGE:
- the default ruler width is now 18 cells
- the last cell of the screen is no longer empty
Closes#41076
259e6fa9cc