process: exit on --debug and --debug-brk after option parsing

Moves the exit of `--debug` and `--debug-brk` earlier, that is,
after the option parsing is done in the C++ land.

Also removes `process._invalidDebug`.

PR-URL: https://github.com/nodejs/node/pull/25828
Refs: https://github.com/nodejs/node/pull/12949


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>