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 <[email protected]>
Co-authored-by: Ujjwal Sharma <[email protected]>
Co-authored-by: Caio Lima <[email protected]>
Co-authored-by: Michael Dyck <[email protected]>
Co-authored-by: Kevin Gibbons <[email protected]>
Co-authored-by: Jordan Harband <[email protected]>