- Add I8x16_Popcnt for WASM SIMD

- Add vcpop_m and vfirst_m for riscv64 simulator

Bug: v8:11976
Change-Id: I2b945bb947da0998663cac86f867f09d386b81a4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3356201Reviewed-by: Yahan Lu <yahan@iscas.ac.cn>
Commit-Queue: Yahan Lu <yahan@iscas.ac.cn>
Cr-Commit-Position: refs/heads/main@{#78444}