Enhance types generation

**Is your feature request related to a problem? Please describe.**

Currently, all types are optional, or at least a lot of them. See: https://github.com/search?q=repo:googleapis/google-api-nodejs-client+%22%7C+null%22&type=code So, this leads to an awful development experience.

For example, see Google Calendar API:

https://github.com/googleapis/google-api-nodejs-client/blob/6e8c998cee93dbc79a6f306c2150414b933c22c9/src/apis/calendar/v3.ts#L720

But on the other hand, we can see in docs that some fields are optional and some are not.

https://developers.google.com/calendar/api/v3/reference/events#resource


**Describe the solution you'd like**
I would like to see real types with the minimum amount of optional fields.

**Describe alternatives you've considered**
Of course, we can check everything manually or disable TypeScript checking at all. But I believe it's not a good solution, as why do we need typings which do not work.
https://github.com/googleapis/google-api-nodejs-client/issues/3151

Beginne mit dem generierten Typ in src/apis/calendar/v3.ts im Bereich des verknüpften Calendar API-Beispiels und vergleiche dann seine optionalen Felder mit der Dokumentation der Google Calendar-Ressource und Issue #3151. Die Aufgabe wäre erledigt, wenn der Typgenerator erforderliche Felder erzeugt, wo die API-Dokumentation sie als erforderlich ausweist, ohne allgemein jedes Feld optional zu machen.

Vom Indexierungsmodell aus dem Issue-Text verfasst.