Cygwin: pty: Trigger redraw screen if ESC[?3h or ESC[?3l is sent.

Cygwin: pty: Trigger redraw screen if ESC[?3h or ESC[?3l is sent.

- Pseudo console clears console screen buffer if ESC[?3h or ESC[?3l
  is sent. However, xterm/vt100 does not clear screen. This cause
  mismatch between real screen and console screen buffer. Therefore,
  this patch triggers redraw screen in that situation so that the
  synchronization is done on the next execution of native app.
  This solves the problem reported in:
  https://www.cygwin.com/ml/cygwin-patches/2019-q4/msg00116.html