[TASK] Clean up various TypeScript code for SVG tree
This change reduces some redundancy in implementations
for drag+drop for pagetree + folder tree,
also adds some comments and adds
some helper methods to make the code
a tiny bit more understandable.
In addition, to reduce our dependencies to
d3-drag, the DragDropHandlers now receive
the node and the original MouseEvent,
as there is nothing else that the DragDrop
handlers need for our solutions.
Tested-by: Oliver Bartsch <firstname.lastname@example.org>
Tested-by: core-ci <email@example.com>
Reviewed-by: Oliver Bartsch <firstname.lastname@example.org>
Tested-by: Andreas Fernandez <email@example.com>
Reviewed-by: Andreas Fernandez <firstname.lastname@example.org>