:redrawstatus does not update the ruler in the last window

[h-east]

Problem:  When the last window has no status line the ruler takes its
          place in the last screen line, but ":redrawstatus" and
          re-setting 'rulerformat' or 'statusline' do not update it
          there.  An item such as a clock in 'rulerformat' can therefore
          not be refreshed from a timer.
Solution: Also mark the ruler for redrawing when the last window has no
          status line and 'ruler' is set.  Update the documentation and
          add a test.

related: https://groups.google.com/g/vim_use/c/VKCL2bH8xlk

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Currently, this is possible with the following setting, but it only updates the status line of the current window when windows are split, and above all, it is not intuitive:

set ruler
set rulerformat=%55(%{strftime('%H:%M:%S')}\ %5l,%-6(%c%V%)\ %P%)
call timer_start(1000, {-> feedkeys("\<Ignore>", 'n')}, {'repeat': -1})

After applying this PR, it would be better to write the third line as follows:

call timer_start(1000, {-> execute(':redrawstatus!')}, {'repeat': -1})

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Notes

The screen dumps of Test_aa_terminal_focus_events had to be updated: they
recorded the ruler as "0,0-1" although the FocusLost/FocusGained
autocommands had already changed the buffer, so the ruler was stale. It
now shows "1,1", which is what a window with a status line showed all
along.