xwm: Use Pango to draw title string if available

xwm: Use Pango to draw title string if available

If Weston is built with Pango, use it to render the title for
X11 applications and Weston toy toolkit clients. It allows us
to ellipsize the title when there isn't enough space to show the
whole string.

Signed-off-by: Louis-Francis Ratté-Boulianne <lfrb@collabora.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>