Extend FloorPlot

[giadarol]

Note that this PR can be merged only after xtrack v0.73.1 is released.

The following modifications and extensions are introduced:

• Plotting the XY projection is now supported.
• The FloorPlot is now generated from the survey table alone without requiring access to the line. This allows plotting the survey after the corresponding line has been modified or deleted. For this purpose additional columns (length, isthick and element_type have been added to the survey table in xtrack v0.73.1.
• The type of magnet is inferred from the element type and not from the strengths. This is to support the common use case in beam-line design, in which one defines a lattice geometry and wants to visualize the positions of the elements before defining the magnetic strengths. A side effect of this modification is that thin elements are all shown as multipoles and in the same color (we could think of doing something more sophisticated in the future, if required by users).

Examples including horizontal and vertical bends are available at https://github.com/xsuite/xplt/blob/extend_floorplot/examples/line_cases.ipynb