This patch makes it possible to set the UI color of a node's
header bar and override the default from the node's typeinfo.
Currently the color is taken from the `.nclass`
member of the node's bNodeType->TypeInfo struct.
This is created once when registering the node.
The TypeInfo is used for both UI and non-UI functionality.
Since the TypeInfo is shared, the header bar for the node
can't be changed without changing all nodes of that type.
The Map Range node is shown as a `Converter` or blue color by default.
This patch allows this to be changed dynamically to `Vector` or purple.
This is done by adding a `ui_class` callback to node typeinfo struct.
Reviewed By: HooglyBoogly
Differential Revision: https://developer.blender.org/D13936
fe4e85a924