Anim: Use Theme for Motion Path points

This PR changes the motion path appearance by using the
`Vertex` color as defined in the 3D viewport theme settings
instead of hardcoding it to white.

The issue with setting it to white is that it is too visually distracting,
overshadowing the points that are keyframes, which are drawn in
the selection color for vertices (also defined in the Theme)

Pull Request: https://projects.blender.org/blender/blender/pulls/119382

source/blender/draw/engines/overlay/shaders/overlay_motion_path_point_vert.glsl

@@ -17,7 +17,7 @@ void main()
 
   int frame = gl_VertexID + cacheStart;
   bool use_custom_color = customColor.x >= 0.0;
-  finalColor = (use_custom_color) ? vec4(customColor, 1.0) : vec4(1.0);
+  finalColor = (use_custom_color) ? vec4(customColor, 1.0) : colorVertex;
 
   /* Bias to reduce z fighting with the path */
   gl_Position.z -= 1e-4;