Web platform integration

There are various web specs which use SetValueInBuffer directly (via WebIDL). These need to be updated and WPT tests written.

Also, there are specs which do a defensive copy of the bytes in a view which can be avoided when the buffer is immutable. This technically is an as-if optimization, but it's probably worth updating the WebIDL and consuming specs to call this out anyway because otherwise people will not know to make this optimization.

See discussion in Matrix.

首先查看链接的 WebIDL SetValueInBuffer 和 get-buffer-source-copy 定义，然后确定使用它们的相关 Web 规范。编写所要求的 WPT 测试，并更新这些规范以处理不可变缓冲区和可避免的防御性复制；使用链接的 Matrix 讨论作为上下文。