Add SIMD support to AArch64 NCG

Motivation

It would be nice if we can use SIMD on AArch64 without requiring LLVM. See also #25030.

Proposal

Add support for 128-bit SIMD to AArch64 NCG with ASIMD (NEON). SVE is not in scope of this proposal, because it is not widely available in consumer devices.

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