patch 9.1.1959: Wrong wrapping of long output using :echowindow

patch 9.1.1959: Wrong wrapping of long output using :echowindow

Problem:  Outputting long strings using :echowindow wraps one character
          per line and display in reverse order (Hirohito Higashi)
Solution: Use full width for :echowindow, reset msg_col after wrapping,
          and increment lnum correctly when creating new lines (glepnir)

fixes: #18750
closes: #18874

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>