Currently our AArch64 backend only supports MulReduction for 64/128 bits vectors by using scalar instructions instead, as it's missing corresponding vector instruction. That's caused a performance gap.

To clarify, the goal of this ticket is to improve the performance of mul reduction VectorAPI operations on SVE-capable platforms with vector lengths greater than 128 bits (e.g., Neoverse V1). The core issue is that these APIs are not being lowered to any AArch64 implementation at all on such platforms. Instead, the fallback Java implementation is used.