LoadMcStas multiple scattering alternative usage example

Following completion of #22458 add LoadMcStas usage example which demonstrates how multiple scattering analysis can alternatively be done using an McStas instrument file setup such as:

COMPONENT nD_Mantid_0 = Monitor_nD(
    options ="mantid square, x limits=[-2.5 2.5] bins=128 y limits=[-2.5 2.5] bins=128, neutron pixel min = 0 t limits [0.002,0.005] list all neutrons, file=all",
    xwidth = 5, yheight = 5, restore_neutron = 1)
  AT (0, 0, 1) RELATIVE sampleMantid

COMPONENT nD_Mantid_1 = Monitor_nD(
    options ="mantid square, x limits=[-2.5 2.5] bins=128 y limits=[-2.5 2.5] bins=128, neutron pixel min = 16384 t limits [0.002,0.005] list all neutrons, file=multi",
    xwidth = 5, yheight = 5, restore_neutron = 1)
  WHEN (multi_flag ==1)
  AT (0, 0, 1) RELATIVE sampleMantid

COMPONENT nD_Mantid_2 = Monitor_nD(
    options ="mantid square, x limits=[-2.5 2.5] bins=128 y limits=[-2.5 2.5] bins=128, neutron pixel min = 32768 t limits [0.002,0.005] list all neutrons, file=single",
    xwidth = 5, yheight = 5, restore_neutron = 1)
  WHEN (single_flag ==1)
  AT (0, 0, 1) RELATIVE sampleMantid

where OutputOnlySummedEventWorkspace = True and individual multiple scattering signals can be extracted from from relevant spectra following the creation of the workspace. The minus of this approach is that it requires users to explicitly extra relevant spectra following LoadMcStas, however, where you have large data and many detector panels it may well become the only practical solution.

Required to do:

Using McStas create small Nexus file with McStas instrument file using code similar to above
Add to Mantid with usage example and documentation

Following merge probably need to also update https://github.com/McStasMcXtrace/McCode/wiki/McStas-and-Mantid

mantidproject / mantid

LoadMcStas multiple scattering alternative usage example #22460