docs(maps): Describe how to get map instance from within component.ts to input to MapMarker, InfoWindow

[SheldonHage]

Documentation Feedback

Currently the example docs rely on a single use case where the user interacts with the map and a (mapClick) event grabs the map instance and passes it back to a component.ts function. If a developer wishes to decorate a map with a marker or an info window before a user interacts with it, there is no map reference to use.

It appears that standard @ViewChild methods for obtaining a dom reference do not work with the angular google-maps component. We could use a good example of how to get the map reference.

Affected documentation page

https://github.com/angular/components/tree/master/src/google-maps/map-marker

[amysorto]

It seems like this was fixed in #23856, I'll leave this issue open to update documentation