Handle texture nodes alternative source rect

Texture nodes has an alternative and rarely used way of setting source
rect using uv_top_left and uv_bottom_right. This patch adds support
for it.

Task-number: QTBUG-59407
Change-Id: Ic14c3dbdede6ece07eb3cda2dcfea8e860654ef2
Reviewed-by: Michael Brüning <michael.bruning@qt.io>