Make sure that fillColor can be only fully opaque

QSafeTextLayout::drawGlyph() algorithm depends on background being fully transparent (the default behaviour without fillColor) or fully opaque (when fillColor is used).

Make sure that tooling makes sure that the fillColor is fully opaque and make sure that Runtime checks and enforces this.

Tests needs to be implemented.

Also, see that opacity can be changed via state change (which should be possible and does not require Runtime to co-operate).

TestRail needs to be updated.