Whenever someone creates a connection to any of the global transform releated
properties for a QQuick3DNode, we inform the scene manager about it. What it
means is that we need to calulate the global transform and emit changes to it
whenever it changes. But knowing when it changes is costly, since it will change
whenever the transform of an ancestor change (and we don't want to listen for
that all the way to the root). So the scene manager will instead delay all global
transform calculations to a be done in a single pass before we update instead.

In many cases there is no time to wait for the scene graph to update before updating
the global matrix for a node. If you e.g change the position of a node, you
need to be able to e.g query to globalPosition right after in order to
position other objects in the scene relative to it. Waiting for the scenegraph
to update will cause such calculations to end up using old values.

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.

The C++ parts don't work for some reason, so right now its just QML
parts.

This is expensive.  Instead we can notify when the global transform has
changed, and then we can return direction vectors on demand.

Added the doc config for the Quick 3D module,
with index and module pages for C++ and QML types.
Also added bare min. docs for a few C++ and QML
types, and a group page for the examples.

Otherwise we wont update the scene on the backend with the new transform
properties

We may want more fine-grained control over visibilty later, but for now
let's assume that a non-visible nodes are inactive nodes.

These got the wrong name from the get-go

converted to radians

Mostly renaming and style changes.