feat(dia.Paper): add methods to find cell/element/link views in paper

[kumilingus]

• feat(dia.Paper): add methods to find cell/element/link views in paper
  • add findCellViewsAtPoint(), findLinkViewsAtPoint(), and findElementViewsAtPoint()`
  • add findCellViewsInArea(), findLinkViewsInArea(), and findElementViewsInArea()`
  • deprecate findViewsFromPoint() and `findViewsInArea()
• feat(dia.Graph): add methods to find cells/elements/links in graph
  • add findCellsAtPoint(), findLinksAtPoint(), and findElementsAtPoint()
  • add findCellsInArea(), findLinksInArea(), and findElementsInArea()
  • add findCellsUnderElement(), findLinksUnderElement(), findElementsUnderElement()
  • deprecate findModelsFromPoint() and findModelsInArea()
• feat(dia.CellView): add isIntersecting() method
• feat(g.Rect): add strict option to containsPoint()

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This PR:

• adds convenience methods for searching for links in the paper based on their geometry.
• optimizes the performance of search for elements and links in the paper.
• allows us to further optimize the search by a more efficient data structure in the graph.
• It lays the foundation for the future implementation of snap-to-link feature (as opposed to existing snap-to-elements).