[CMake] Renamed BUILD_TESTING to OGS_BUILD_TESTING.

Applications/Utils/CMakeLists.txt

CMakeLists.txt

ProcessLib/ComponentTransport/CMakeLists.txt

ProcessLib/HT/CMakeLists.txt

ProcessLib/HT/Tests.cmake

ProcessLib/HeatConduction/CMakeLists.txt

ProcessLib/HeatTransportBHE/CMakeLists.txt

ProcessLib/HydroMechanics/CMakeLists.txt

ProcessLib/LIE/CMakeLists.txt

ProcessLib/LiquidFlow/CMakeLists.txt

ProcessLib/PhaseField/CMakeLists.txt

ProcessLib/RichardsComponentTransport/CMakeLists.txt

ProcessLib/RichardsFlow/CMakeLists.txt

ProcessLib/RichardsMechanics/CMakeLists.txt

ProcessLib/SmallDeformation/CMakeLists.txt

ProcessLib/SmallDeformationNonlocal/CMakeLists.txt

ProcessLib/TES/CMakeLists.txt

ProcessLib/ThermalTwoPhaseFlowWithPP/CMakeLists.txt

ProcessLib/ThermoHydroMechanics/CMakeLists.txt

ProcessLib/ThermoMechanicalPhaseField/CMakeLists.txt