src: simplify inspector initialization in node::Start()

Remove the `StartInspector` and `InspectorStarted` abstraction
out of `v8_platform`, and error out early and directly in the
option parser if Node is configured with NODE_USE_V8_PLATFORM and
inspector enabled but the user still tries to use inspector options.

PR-URL: https://github.com/nodejs/node/pull/25612


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>