Spanify MaskWebSocketFramePayload method to avoid unsafe buffer usage

This CL spanifies the `MaskWebSocketFramePayload` and
`MaskWebSocketFramePayloadByBytes` methods, replaces unchecked pointers
with `base::span`, and enables unsafe-buffer-usage warnings in
`websocket_frame`.

Bug: 40284755,354307327
Change-Id: I98710ab69174ef6d2049a7deaf6d203c528101ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5764863
Reviewed-by: Alex Rudenko <alexrudenko@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Commit-Queue: kelsen liu <kelsenliu21@gmail.com>
Reviewed-by: Adam Rice <ricea@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1343917}