Separate and fix 8/24-bit text mask materials.

Separate and fix 8/24-bit text mask materials.

The logic was a bit cluttered, trying to handle two rather
different pieces of logic in one material shader. The 8-bit
shader does not try to be fancy in any way, it just takes the
alpha * color which gives similar intensities as the distance
fields. The logic for 24-bit contains a tiny fix for opacity.

The patch also includes a change from QColor -> QVector4D and
QPointF -> QVector2D to simplify the conversion needed and
be consistent with what kind of types we use.

Task-number: QTBUG-33805
Task-number: QTBUG-33633
Task-number: QTCREATORBUG-10176
Change-Id: Ia8c464f98a1fc2c190a1d323fc21466a4d7b0dfd
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>