qt: seam observed in pointing tooltip

When "vertex" antialiasing is used (default), a seam might be observed.

Possible solutions:

• Use multi sampling antialiasing.
• Disable rounding. When rounding is disabled, vertex AA is not engaged.

Why not;

• Use Shape instead of Rectangle for drawing the triangle, or the whole shape? No support for "vertex" AA as in Rectangle.
• Use custom scene node for a triangle? Need to reimplement the wheel (for MSAA rather use Shape, for vertex little benefit against not using Rectangle)

Personal opinion, we should opt in 4 samples MSAA by default. It is almost always hardware accelerated. Benefits of MSAA already discussed but mainly there will be much less blending required. "Vertex" AA works by fading out the outline of the edges, which in turn requires using alpha primitives. Less blending also has the benefit of inducing more effective batching.