Fix for ATR-28066 : Temporarily re-add gSuperCellTowerMapper to gFEXDriver
This MR is meant to fix the Run2 test error reported in ATR-28066. It does not solve the real problem underneath.. It is meant to quickly restore the test - so @ctosciri will have more time to clean up the gFEXDriver algorithm.
Also discussed in !64533 (comment 7007367)