McXtrace: Work toward fixing #2514 (GPU)

[willend]

Free-form text area

Please describe what your PR is adding in terms of features or bugfixes:

• Rectification of Multilayer_elliptic for use on GPU
• Simplification of t_Reflec

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Development OS / boundary conditions

Please describe what OS you developed and tested your additions on, and if any special dependencies are required:

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PR Checklist for contributing to McStas/McXtrace

For a coherent and useful contribution to McStas/McXtrace, please fill in relevant parts of the checklist:

• My contribution includes patches to an existing component file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the component (please attach as screenshot in comments!)
  • I have ensured that basic use of the component is OK (e.g. an instrument using it compiles?)
  • I have used the mctest utility to test one or more instruments making use of the component (please attach mcviewtest report as screenshot in comments)
  • I have used the mccode-clangformat tool to apply the standard McCode component indentation scheme
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised

• My contribution includes patches to an existing instrument file

  • I have used the mcdoc utility and rendered a reasonable documentation page for the instrument (please attach as screenshot in comments!)
  • I have used the mctest utility to test the instrument (please attach mcviewtest report as screenshot in comments)
  • I have used the mcrun --c-lint "linter" and followed advice to remove most / all warnings that are raised

• My contribution contains something else

  • Explanation is added in free form text above or below the checklist

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