Animation: Match Slope slider

It blends selected keys to the slope of neighboring ones.
It is used to push the segment closer to the values of the next or previous pose.

Co-authored-by: Ares Deveaux <aresdevo@gmail.com>
Pull Request: https://projects.blender.org/blender/blender/pulls/110567

scripts/startup/bl_ui/space_graph.py

@@ -301,6 +301,7 @@ class GRAPH_MT_key_blending(Menu):
         layout.operator("graph.ease", text="Ease")
         layout.operator("graph.blend_offset", text="Blend Offset")
         layout.operator("graph.blend_to_ease", text="Blend to Ease")
+        layout.operator("graph.match_slope", text="Match Slope")
 
 
 class GRAPH_MT_key_smoothing(Menu):