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