Compositor: Cryptomatte compositing node.

This patch adds a new matte node that implements the Cryptomatte specification.
It also incluces a custom eye dropper that works outside of a color picker.
Cryptomatte export for the Cycles render engine will be in a separate patch.

Reviewers: brecht

Reviewed By: brecht

Subscribers: brecht

Tags: #compositing

Differential Revision: https://developer.blender.org/D3531

release/scripts/startup/nodeitems_builtins.py

@@ -394,6 +394,7 @@ compositor_node_categories = [
         NodeItem("CompositorNodeChromaMatte"),
         NodeItem("CompositorNodeColorMatte"),
         NodeItem("CompositorNodeDoubleEdgeMask"),
+        NodeItem("CompositorNodeCryptomatte"),
     ]),
     CompositorNodeCategory("CMP_DISTORT", "Distort", items=[
         NodeItem("CompositorNodeScale"),