[EMCAL-604] Initialize Unit Tests for the EMCal Geometry class

[nstrangm]

• GetCellIndex as first function to be tested:
  • Check sm number, module number, phi and eta index for all valid cells
  • Check two exceptions for invalid cells
  • Check against on-the-fly calculation in the testGeometry.cxx file itself
• Minor correction in Geometry.cxx to improve readability of the code

[github-actions]

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[mfasDa]

Looks good