src: reorganize inspector and diagnostics initialization

- Split the initialization of the inspector and other diagnostics
  into `Environment::InitializeInspector()` and
  `Environment::InitializeDiagnostics()` - these need to be
  reinitialized separately after snapshot deserialization.
- Do not store worker url alongside the inspector parent handle,
  instead just get it from the handle.
- Rename `Worker::profiler_idle_notifier_started_` to
  `Worker::start_profiler_idle_notifier_` because it stores
  the state inherited from the parent env to use for initializing
  itself.

PR-URL: https://github.com/nodejs/node/pull/27539


Reviewed-By: Anna Henningsen <anna@addaleax.net>