debugger: wait for V8 debugger to be enabled

Refs: https://github.com/nodejs/node/pull/38273#issuecomment-848438189

PR-URL: https://github.com/nodejs/node/pull/38811


Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Beth Griggs <bgriggs@redhat.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>