The Node Context Menu contains options that are not always available for
the selected nodes, and misses important entries for accesibility.
This patch covers the following:
* Add operators to join and remove nodes from frames.
* Sort and group entries more logically and follow Blender conventions.
* Add `Insert into Group`
* Show group actions only on nodes that support it.
* Move all toggles to a sub-menu called `Show/Hide`.
* When nothing is selected, show Add menu, links actions, and paste.
Inspired by RightClickSelect proposals and community feedback.
See D16216 for images.
Reviewed By: HooglyBoogly
Differential Revision: https://developer.blender.org/D16216
2c096f17a6