Implement the S.R.I.VectorXXX `get_Zero` and `As` helper methods as JIT intrinsics...

Implement the S.R.I.VectorXXX `get_Zero` and `As` helper methods as JIT intrinsics (dotnet/coreclr#21198)

* Remove ARM64_SIMD_StaticCast intrinsic and the x86 TwoTypeGeneric flag

* Implementing the `S.R.Intrinsic.VectorXXX.As` methods as runtime intrinsics

* Implementing the get_Zero method on the S.R.Intrinsic.VectorXXX types as runtime intrinsics

Commit migrated from https://github.com/dotnet/coreclr/commit/42ac3d30b1d8310e13eab6f42cc754fa53c5a01d