tests: refactor Array test files.
* move all ObjC array tests into a separate file ArraysObjc.swift.gyb
* merge the remaining Arrays.swift.gyb and ArrayNew.swift.gyb files
* move the utilities from ArrayTypesAndHelpers.swift into its only use into ArraysObjc.swift.gyb
(cherry picked from commit 6f4192927e2c5534e17be9d31cbf718a06c34fed)
(cherry picked from commit 703c354f29746a96859443766611d626164c12d2)
