Split out OrdinaryDiffEqCore and make dependencies into a tree #3743

Job	Run time
test (InterfaceI, 1)	20m 39s
test (InterfaceII, 1)	25m 6s
test (InterfaceIII, 1)	15m 37s
test (Integrators_I, 1)	21m 17s
test (AlgConvergence_I, 1)	11m 44s
test (AlgConvergence_II, 1)	9m 13s
test (AlgConvergence_III, 1)	12m 48s
test (Downstream, 1)	11m 17s
test (ODEInterfaceRegression, 1)	12m 11s
test (Multithreading, 1)	13m 56s
test (OrdinaryDiffEqAdamsBashforthMoulton, 1)	11m 0s
test (OrdinaryDiffEqBDF, 1)	13m 38s
test (OrdinaryDiffEqCore, 1)	9m 34s
test (OrdinaryDiffEqDefault, 1)	9m 47s
test (OrdinaryDiffEqDifferentiation, 1)	9m 26s
test (OrdinaryDiffEqExplicitRK, 1)	9m 31s
test (OrdinaryDiffEqExponentialRK, 1)	13m 2s
test (OrdinaryDiffEqExtrapolation, 1)	11m 50s
test (OrdinaryDiffEqFIRK, 1)	11m 59s
test (OrdinaryDiffEqFeagin, 1)	11m 27s
test (OrdinaryDiffEqFunctionMap, 1)	9m 38s
test (OrdinaryDiffEqHighOrderRK, 1)	10m 14s
test (OrdinaryDiffEqIMEXMultistep, 1)	9m 42s
test (OrdinaryDiffEqLinear, 1)	11m 44s
test (OrdinaryDiffEqLowOrderRK, 1)	11m 9s
test (OrdinaryDiffEqLowStorageRK, 1)	17m 4s
test (OrdinaryDiffEqNordsieck, 1)	11m 36s
test (OrdinaryDiffEqPDIRK, 1)	9m 40s
test (OrdinaryDiffEqPRK, 1)	9m 27s
test (OrdinaryDiffEqQPRK, 1)	10m 59s
test (OrdinaryDiffEqRKN, 1)	12m 2s
test (OrdinaryDiffEqRosenbrock, 1)	16m 52s
test (OrdinaryDiffEqSDIRK, 1)	9m 47s
test (OrdinaryDiffEqSSPRK, 1)	12m 57s
test (OrdinaryDiffEqStabilizedIRK, 1)	10m 41s
test (OrdinaryDiffEqStabilizedRK, 1)	12m 51s
test (OrdinaryDiffEqSymplecticRK, 1)	17m 42s
test (OrdinaryDiffEqTsit5, 1)	9m 47s
test (OrdinaryDiffEqVerner, 1)	9m 38s
	8h 8m 32s

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