Restructured the reading of the high order grids for the FEM solver #8264

Job	Run time
Build SU2 (asan) (BaseNoMPI-asan)	16m 51s
Build SU2 (BaseMPI)	13m 12s
Build SU2 (asan) (ReverseNoMPI-asan)	44m 30s
Build SU2 (ReverseMPI)	14m 30s
Build SU2 (ForwardMPI)	11m 36s
Build SU2 (BaseNoMPI)	7m 47s
Build SU2 (tsan) (BaseOMP-tsan)	11m 49s
Build SU2 (ReverseNoMPI)	12m 35s
Build SU2 (tsan) (ReverseOMP-tsan)	29m 22s
Build SU2 (ForwardNoMPI)	9m 54s
Build SU2 (BaseOMP)	8m 1s
Build SU2 (ReverseOMP)	15m 23s
Build SU2 (ForwardOMP)	10m 19s
Unit Tests (test_driver)	50s
Regression Tests (vandv.py)	2m 26s
Unit Tests (test_driver_AD)	51s
Regression Tests (tutorials.py)	6m 3s
Unit Tests (test_driver_DD)	52s
Regression Tests (parallel_regression.py)	13m 29s
Regression Tests (parallel_regression_AD.py)	9m 27s
Regression Tests (serial_regression.py)	16m 24s
Regression Tests (serial_regression_AD.py)	6m 6s
Regression Tests (hybrid_regression.py)	10m 58s
Regression Tests (hybrid_regression_AD.py)	3m 32s
Thread Sanitizer Tests (hybrid_regression.py)	26m 16s
Thread Sanitizer Tests (hybrid_regression_AD.py)	10m 48s
Address Sanitizer Tests (serial_regression.py)	15m 14s
Address Sanitizer Tests (serial_regression_AD.py)	6m 3s
	5h 35m 8s

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