buffer: add Blob.prototype.stream method and other cleanups

Adds the `stream()` method to get a `ReadableStream` for the `Blob`.
Also makes some other improvements to get the implementation closer
to the API standard definition.

Signed-off-by: James M Snell <jasnell@gmail.com>

PR-URL: https://github.com/nodejs/node/pull/39693


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Bradley Farias <bradley.meck@gmail.com>
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>