Function core::arch::wasm64::i16x8_extend_low_i8x16

pub fn i16x8_extend_low_i8x16(a: v128) -> v128

Available on target_family="wasm" and target feature simd128 and WebAssembly only.

将较小 lane vector 的下半部分转换为较大 lane vector，并扩展符号。