Merge branch 'geometry-nodes' into geometry-nodes-transform-node

Cleanup: Remove unused variable

Merge branch 'master' into geometry-nodes

Geometry Nodes: Add transform geometry node

Merge branch 'master' into geometry-nodes

Geometry Nodes: make some function nodes available

We might not want to have all those nodes in a final version.
Some of them have been added with particle nodes in mind.
However, to test the evaluation system it is useful to have a
couple of nodes available.

Those nodes should "just" work, because their implementation
is reused from the particle nodes project.

Geometry Nodes: improve node group evaluation

This adds support for nodes that have a multi-function implementation.
That includes various function nodes like Math, Combine Vector, ...

Furthermore, there is support for implicit conversions now. So it should
work when one connects e.g. a float to an integer and vice versa.

Nodes: add utility methods

Functions: add utility method

Geometry Nodes: Resolve some missing 3D viewport updates

These two functions "snode_notify" and "ED_node_tag_update_id" appear to
be mostly duplicates. However, there is already a case for each type of
built-in node tree, so it makes sense to add one for the geometry node
tree as well. This doesn't solve the update issues for changing number
in buttons, that must be handled somewhere else.

Merge branch 'master' into geometry-nodes

Geometry Nodes: Add edge split node functionality

Geometry Nodes: expose minimum vertices input of Triangulate node

Fix error in previous commit

That should not have happened -.-

Fix previous comment

Geometry Nodes: simplify and deduplicate callbacks on sockets

This adds a layer of abstraction between the code calling callbacks
on sockets and the implementation of those callbacks.
This abstraction layer allows some sockets to not implement all
callbacks when those can be derived from some other callback.

Geometry Nodes: change "Node Tree" to "Node Group"

Geometry Nodes: initial support for evaluating geometry node groups

This is still very basic and does quite a few unnecessary computations.
Also the error handling is quite weak currently, so when invalid things are
connected, it will probably just crash.

Also the interface that individual nodes have to implement will have to change,
but the current solution is a good starting point.

Only the triangulate node is implemented for now.

Geometry Nodes: add an initial geometry class

Functions: add generic pointer class

This class represents a pointer whose type is only known at runtime.