use data type and domain enum in random attribute node

initial attribute creation

initial WriteAttribute

initial random attribute node

cleanup

simplify typed access

cleanup

cleanup naming

cleanup

use simpler accessor

initial working version

wip

Geometry Nodes: simplify GeometrySet ownership handling

Previously, GeometrySets and GeometryComponents has reference
counters and could be shared. This commit changes it so that
only GeometryComponents are shared. A GeometrySet is a fairly
small type that is cheap to copy.

A lot of code simplifies when we can assume that GeometrySet
is cheap to copy.

Geometry Nodes: Move GeometrySet classes to global namespace

Brecht and I decided to move the GeometrySet classes
to the global namespace for now. This way we can use
the same type in C and C++ and don't have to use
reinterpret_cast as often.

Merge branch 'master' into geometry-nodes

Geometry Nodes: Improve node group output modifier error

More than output for the modifier's node group is fine, because the
node group may be used in other situations, but the modifier will
not work if there is no geometry output socket.

Merge branch 'master' into geometry-nodes

Empty Modifier: Fix build and put in the right order

Bypassing the macro that creates modifiers to allow the enum to be
referring to the Empty modifier, but the internal struct in the code to
be Nodes.

Also fix the name of the new created modifiers to be "Empty".

Fix was built with rBb458ea6b23381a9acb90dbbd73ced678e1d404c5.

Rename: "Nodes" modifier to "Empty" (take 2)

Leave the internal DNA data struct as "Nodes", and only rename the
modifier and user interface to Empty.

See 4a2734a835c10d5bffaaceddc59c for the original take and the reasoning
for renaming from Nodes to Empty.

Revert "Rename: "Nodes" modifier to "Empty""

This reverts commit 4a2734a835c10d5bffaaceddc59c41837801f402.

Reverting this so that all we change is the UI name, not the DNA struct
and the internal variable names.