Fix ATLITKSW-124. Remove the implementation for the invalid combination of...

Fix ATLITKSW-124. Remove the implementation for the invalid combination of Condensed (DataReadOutMode=0) and X1X (DataCompressionMode=1). Modify the code to abort jobs if invalid combinations are used. Define and use enums of CompressionMode and ReadOutMode for easier understanding.

InnerDetector/InDetDigitization/SCT_Digitization/src/SCT_FrontEnd.h

 /*
-  Copyright (C) 2002-2017 CERN for the benefit of the ATLAS collaboration
+  Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
 */
 
 /**
@@ -89,6 +89,9 @@ class  SCT_FrontEnd : public AthAlgTool, virtual public ISCT_FrontEnd {
 
  private:
 
+  enum CompressionMode { Level_X1X=1, Edge_01X=2, AnyHit_1XX_X1X_XX1=3 }; // Used for m_data_compression_mode (DataCompressionMode)
+  enum ReadOutMode { Condensed=0, Expanded=1 }; // Used for m_data_readout_mode (DataReadOutMode)
+
   bool m_PulseAveragingFlag;
 
   float m_NoiseBarrel ;                     //!< Noise factor, Barrel  (in the case of no use of calibration data)