This PR and commit adds the functionality to arrange nodes in VisualScript/VisualShader editor. The layout generated by this
feature is compact, with minimum crossings between connections
& uniform horizontal & vertical gaps between the nodes.
This work has been sponsored by GSoC '21.
Full list of additions/changes:
• Added arrange_nodes() method in GraphEdit module.
• This method computes new positions for all the selected
nodes by forming blocks and compressing them.
The nodes are moved to these new positions.
• Adding this method to GraphEdit makes it available for
use in VisualScript/VisualShaders editors and its other
subclasses.
• Button with an icon has been added to call arrange_nodes() in GraphEdit.
• This button is inherited by VisualScript/VisualShaders editors
to invoke the method.
• Undo/redo is functional with this method.
• By using signals in arrange_nodes(), position changes are registered
in undo/redo stack of the subclass that is using the method.
• Metadata of the method has been updated in ClassDB
• Method description has been added to class reference of GraphEdit
