darwin/arm64: fix SIMD detection and improve ARM feature probing

[HippoBaro]

Detection of Advanced SIMD (NEON) on M1 Macs was broken due to querying
the wrong sysctl identifier. Apple's documentation lists
"hw.optional.AdvSIMD" as the correct identifier, but in reality, it's
"hw.optional.arm.AdvSIMD" as confirmed by `sysctl -a`. This patch
corrects the identifier and adds support for its alias, "hw.optional
.neon," ensuring proper detection across all models.

Additionally, this patch revisits all ARM features detected by the
package, cross-referencing identifiers (and aliases) against both
Apple's official sysctl documentation:
  https://developer.apple.com/documentation/kernel/1387446-sysctlbyname/determining_instruction_set_characteristics
and the ARM architecture reference manual:
  https://developer.arm.com/documentation/ddi0487/latest

Each ARM feature now maps to all known sysctl aliases, preventing false
negatives and improving detection accuracy on Apple Silicon.

[klauspost]

LGTM. Thanks for the contribution! <3