MuonGeoModelR4 - Use GeoModelTree to retrieve the cutouts

• Introduced the IGeoModelUtilityTool providing helper function to retrieve the shapes & children
• MdtTubeLayer class browses through the GeoModel tree to determine the tube positions and their respective lengths
• MdtCut is no longer needed because the cuts are implemented in the GeoModel upstream already

I've tested the BIL1A13 chamber. The new readout geometry gives exactly the same tube centers as the old one. There're still subtle differences in the tube length because the D1 from the AMDB tables is never parsed to an auxillary table.

*-- Definition of BIL stations -------------------------------------------------
* Typ I  No
*  dx     dy     dz  Io Tec i x y s  W_xS    W_xL     L_y     Ex     D1     D2
* ...
D BIL 1   7
   0.     0.     0.   1 MDT 1       2671.5  2671.5 1081.261   0.    55.     0.
-1280.    0.   123.07 2 CHV 1          6.0     6.0 1081.261   0.     0.     0.
   0.     0.   123.07 3 CMI 1          6.0     6.0 1081.261   0.     0.     0.
1280.     0.   123.07 4 CRO 1          6.0     6.0 1081.261   0.     0.     0.
   0.   215.   170.57 5	LB  1       2620.0  2620.0    50.     0.     0.     0.
   0.   815.   170.57 6	LB  1       2620.0  2620.0    50.     0.     0.     0.
   0.     0.   293.07 7 MDT 2       2671.5  2671.5 1081.261   0.    55.     0.

Tagging: @boudreau, @tsulaia, @rbianchi, @dellacqu, @smeriano