inspector: reimplement JS binding

- Group all relevant methods/states into a C++ class.
- Uses internal fields instead of the less efficient v8::External for
  storing the pointer to the C++ object.
- Use AsyncWrap to allow instrumenting callback states.

PR-URL: https://github.com/nodejs/node/pull/15643
Refs: https://github.com/nodejs/node/issues/13503


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>