buffer: move initialization of buffer prototype into node.js

Instead of exposing it in `lib/internal/buffer.js` after deleting
it from the binding and then do the initialization in
`lib/buffer.js`, which results in an implicit dependency on
the order in which these modules are loaded.

PR-URL: https://github.com/nodejs/node/pull/25292


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>