Provides an interface for dragging and dropping <see cref="T:Editor.Asset" /> or <see cref="T:Sandbox.Package" /> on a map view. Use with <see cref="T:Editor.MapEditor.CanDropAttribute" /> to register your drop target for a <see cref="T:Sandbox.Package.Type" /> or <see cref="T:Sandbox.GameResource" /> type.