Not fully. Really what happened is they did a re-org that gave them Google Cloud as an umbrella brand including GCP, Google Maps Platform (this new version of Google Maps as a commercial service), Chrome, Android, G Suite...
The bit of Maps Platform integration for management of the billing and API layer was called out in the announcement blog as an integration with the console specifically, and the docs and other branding around Maps Platform remain distinct from GCP still in excessively subtle ways that Googlers pay more attention to than everyone else, like hosting the docs on developers.google.com instead of cloud.google.com and having Platform in its name separately from Cloud Platform.
This stuff makes sense to Googlers not only because of the org chart but also because Google has a pretty unified API layer technology and because Google put in a lot of work to unify billing tech & management. Reusing that is efficient but not always clear.
But you're right to be confused. Their branding is a mess and always has been. This is the same company that thought Google Play Books makes sense as a product name.
Google's product / PR / comms / exec people are very bad at understanding how external people who don't know Google's org chart and internal tech will perceive these things, or at least bad at prioritizing those concerns.
They live and breathe their corporate internals too much to realize this. Some Google engineers and tech writers realize the confusion but pick other battles to fight instead (like making good quality products).
They do at least document which services are subjected to the GCP Deprecation Policy (Maps is not there): https://cloud.google.com/terms/deprecation
As for what products are actually part of GCP, it's the parts of this page that aren't an external partner's brand name, aren't called out separately like G Suite or Cloud Identity or Cloud Search, and aren't purely open source projects like Knative and Istio (as opposed to the productized versions within GCP), with the caveat that the level so far of integration into GCP of Google acquisitions like Apigee, Firebase, and Stackdriver varies depending on per-company specifics: https://cloud.google.com/products/
G Suite and Cloud Identity accounts can be used with GCP, just like any other Google accounts. They are part of Google Cloud but not Google Cloud Platform.
Hope I waded through the mess correctly for you. :)