Function core::arch::wasm32::i16x8_extend_high_i8x16

pub fn i16x8_extend_high_i8x16(a: v128) -> v128

This is supported on WebAssembly and target feature simd128 only.

将较小通道 vector 的高一半转换为较大通道 vector，并对其进行符号扩展。