Split off from D9054
This patch adds a "Blend To Neighbour" Operator to the pose sliding tools.
**Problem**
When animating you often want to nudge your current pose to the neighbouring poses slightly.
The breakdowner would override the current pose completely.
**Solution**
Instead of interpolating between the left and right key, this operator interpolates from the current pose to either left or right, depending if the percentage is bigger or smaller than 50%.
This graphic should explain how it works compared to the Breakdowner
{F9004237}
There is a menu entry for the new operator. It is also registered under the ALT + SHIFT + E hotkey
{F8965044}
**Limitations and future improvements**
POSE_OT_blend_to_neighbours doesn't respect an unkeyed position. In fact none of the operators do, but this hasn't been an issue until now.
The tools still only work in pose mode. It would be good for them to work in object mode as well.