docs(google-maps): use inject() instead of constructor injection in examples

[yogeshwaran-c]

What kind of change does this PR introduce?

Documentation update.

What is the current behavior?

The MapGeocoder and MapDirectionsRenderer README examples use constructor
injection to obtain services. The MapDirectionsRenderer example is also
missing the import {map} from 'rxjs/operators' import and has inconsistent
indentation on the imports array.

What is the new behavior?

• Use inject() instead of constructor injection, consistent with the modern
  Angular standalone pattern used across the rest of the docs.
• Add the missing import {map} from 'rxjs/operators' to the directions
  renderer example so the code compiles as shown.
• Fix indentation of the imports array in the directions renderer example.
• Simplify the directions renderer example by using a field initializer instead
  of assigning inside the constructor.

Additional context

Both MapGeocoder and MapDirectionsService are providedIn: 'root', so they
work with inject() without any additional provider configuration.