SplineTest: cleanup identity tests with INSTANTIATE_TEST_CASE_P+template
SplineTest: cleanup identity tests with INSTANTIATE_TEST_CASE_P+template

LebedevRI/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed