Problem:    Only a change in the current window triggers the WinScrolled
            event.
Solution:   Trigger WinScrolled if any window scrolled or changed size.
            (issue #11576)

Problem:    libvterm with modifyOtherKeys level 2 does not match xterm.
Solution:   Adjust key code escape sequences to be the same as what xterm
            sends in modifyOtherKeys level 2 mode.  Check the value of
            no_reduce_keys before using it.

Problem:    With 'smoothscroll' set mouse click position may be wrong.
Solution:   Adjust computations for w_skipcol. (Yee Cheng Chin, closes #11514)

Problem:    Setting lines in another buffer may not work well.
Solution:   Make sure the buffer being changed has a window. (issue #11558)

Problem:    Error message for layout change does not match action.
Solution:   Pass the command to where the error is given. (closes #11573)

Problem:    With 'smoothscroll' cursor may end up in wrong position.
Solution:   Correct the computation of screen lines. (Yee Cheng Chin,
            closes #11502)

Problem:    Restoring window after WinScrolled may fail.
Solution:   Lock the window layout when triggering WinScrolled.

Problem:    Mouse scroll code is not optimal.
Solution:   Properly organise Normal mode, Insert mode and common code.
            (Christopher Plewright, closes #11572)

Problem:    Virtual text after the line wraps when 'wrap' is off.
Solution:   Only set text_prop_follows when wrapping. (closes #11463)

Problem:    Various comment and indent flaws.
Solution:   Improve comments and indenting.