patch 9.2.0907: popup: virtual text is not redrawn when a text property changes

patch 9.2.0907: popup: virtual text is not redrawn when a text property changes

Problem:  Adding or removing a text property in the buffer of a popup
          window does not update the popup on the screen.  The old
          virtual text stays visible until something else causes a
          redraw.
Solution: Also mark popup windows displaying the buffer for redrawing in
          redraw_buf_later() (Hirohito Higashi).

fixes:  #19297
closes: #20931

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Signed-off-by: Hirohito Higashi <h.east.727@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>