This commit makes links connected to multi-input sockets spread verticaly
along the socket. Sockets grow if more links are connected and the node
layout updates accordingly. Links are sorted by their incoming angle
to avoid crossing links. Also, link picking is updated to work with
spread links and bezier links.
Currently the multi-input sockets are used in the join geometry node.
The mutli-input sockets look like a vertical rounded rectangle.
Currently they do not support the other custom socket shapes.
Reviewed By Hans Goudey, with cleanup and additional edits
Differential Revision: https://developer.blender.org/D10181
8f707a72e8