Nodes: add "Mix Vector" to Shader Editor Add menu

The Mix node has multiple subtypes for handling different data types. (Float, Color, Vector, etc.)

Since these are commonly used operations, the different subtypes are made easily accessible
under the names "Mix Color" & "Mix Vector". These are mostly present in the various node
editors. (Shader, Geometry, & Compositing)

Notably, for Shader Nodes, however, only the "Mix Color" entry is present in the Add Menu.
This patch adds the missing "Mix Vector" entry under the "Vector" category of the
Shader Editor Add Menu.

Pull Request: https://projects.blender.org/blender/blender/pulls/142886

scripts/startup/bl_ui/node_add_menu_shader.py

@@ -366,6 +366,10 @@ class NODE_MT_shader_node_vector_base(node_add_menu.NodeMenu):
         self.node_operator(layout, "ShaderNodeBump")
         self.node_operator(layout, "ShaderNodeDisplacement")
         self.node_operator(layout, "ShaderNodeMapping")
+        props = self.node_operator(layout, "ShaderNodeMix", label="Mix Vector")
+        ops = props.settings.add()
+        ops.name = "data_type"
+        ops.value = "'VECTOR'"
         self.node_operator(layout, "ShaderNodeNormal")
         self.node_operator(layout, "ShaderNodeNormalMap")
         self.node_operator(layout, "ShaderNodeRadialTiling")