Automatic arrangement of nodes in VisualScript/VisualShaders editors

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

0 files changed, 0 insertions, 0 deletions