Breakdown Implementation

This patch adds the breakdown (or tween) functionality to the graph editor.

The factor defines the linear interpolation from left key to right key.

Reviewed by: Sybren A. Stüvel
Differential Revision: https://developer.blender.org/D9375
Ref: D9375

release/scripts/startup/bl_ui/space_graph.py

@@ -344,7 +344,8 @@ class GRAPH_MT_slider(Menu):
 
     def draw(self, _context):
         layout = self.layout
-
+        
+        layout.operator("graph.breakdown", text="Breakdown")
         layout.operator("graph.blend_to_neighbor", text="Blend To Neighbor")