[AArch64][LV][SLP] Vectorizers use call cost for vectorized frem (#82488)

getArithmeticInstrCost is used by both LoopVectorizer and SLPVectorizer
to compute the cost of frem, which becomes a call cost on AArch64 when
TLI has a vector library function.

Add tests that do SLP vectorization for code that contains 2x double and
4x float frem instructions.