Blender Git Loki

Nodes: Move group input and output to a consistent menu location

Currently (in geometry nodes) you can delete the group input or group
output nodes with no way to get them back without copy and paste. This
adds them to the "Group" submenu of the add menu so at least there is
a way to add them back.

Additionally, these nodes are moved to the "Group" submenu for all node
editors. This makes sense since they are not like the other input or
output nodes, they really just relate to how groups are organized.

Differential Revision: https://developer.blender.org/D10241