Normative: Add public and private class fields, static class features…

…, private methods & getters/setters

This includes changes from https://tc39.es/proposal-class-fields/.
This includes changes from https://tc39.es/proposal-private-methods/.
This includes changes from https://tc39.es/proposal-static-class-features/.

Co-authored-by: Ms2ger <Ms2ger@gmail.com>
Co-authored-by: Ujjwal Sharma <ryzokuken@igalia.com>
Co-authored-by: Caio Lima <ticaiolima@gmail.com>
Co-authored-by: Michael Dyck <jmdyck@ibiblio.org>
Co-authored-by: Kevin Gibbons <bakkot@gmail.com>
Co-authored-by: Jordan Harband <ljharb@gmail.com>