Only works when using tesselation shaders

This enables finer control of how the scene is shadowed, and can lead to
better performance tuning and quality.

This really doesn't make sense.  Instead I provided an example of how
this is suppose to work in Qt Quick.  Bonus is that we get 22 modes
instead of the 8 supported by 3DS.

We can do much better, but for the time being since we have zero input
support for 3D here is some basic plumbing it get some picking going.

Ideally we would not need this at all, but will need to come up with a
better solution later.

These are examples of non-public API and are in practice manual tests of
that API.

Adds a CameraDirty entry to QDemonRenderNode::Flag. It already has
Orthographic, so if it should move then they can move together.

Camera now stores the previous viewport and design dimensions it
calculated projection with so we can avoid the calculation completely
if nothing changed.

After having initially enabled it.

Also some drive-by changes:

- Remove always-true nullptr check
- Only go through the loadRenderImage-branch if we were dirty

Just a small utility to save lines when doing conditional assignment
and work based on equality. Used in follow-up patches.

Includes new sourceItem property on Texture

Drive-by change