Shading: Add Clamp node to Cycles and EEVEE.

This patch adds a new node that clamps a value between a maximum and
a minimum values.

Reviewers: brecht

Differential Revision: https://developer.blender.org/D5476

release/scripts/startup/nodeitems_builtins.py

@@ -259,6 +259,7 @@ shader_node_categories = [
     ]),
     ShaderNodeCategory("SH_NEW_CONVERTOR", "Converter", items=[
         NodeItem("ShaderNodeMapRange"),
+        NodeItem("ShaderNodeClamp"),
         NodeItem("ShaderNodeMath"),
         NodeItem("ShaderNodeValToRGB"),
         NodeItem("ShaderNodeRGBToBW"),