New principle: accept arrays of bytes as BufferSource

[bakkot]

I wanted to make sure this is captured from the discussion here, even though I'm personally neutral on it as a principle and therefore don't want to be the one to write it up (I kind of prefer accepting only Uint8Array and ArrayBuffer because, for example, it is ambiguous how to interpret a Uint16Array as a sequence of bytes). It is currently an almost-universal convention.

I also think it would be good to specify that [AllowShared] and [AllowResizable] should be the defaults for BufferSource-taking APIs, even though very few existing APIs have been updated with those attributes yet.