Added Google Maps sample code (#1671)

* Added Google Maps sample code

* Updated per @domesticmouse review

* Updated dependabot and pubspec for Dart 2.19

google_maps/pubspec.yaml

@@ -0,0 +1,26 @@
+name: google_maps_in_flutter
+description: A new Flutter project.
+publish_to: 'none' 
+version: 1.0.0+1
+environment:
+  sdk: '>=2.19.0 <3.0.0'
+dependencies:
+  flutter:
+    sdk: flutter
+  cupertino_icons: ^1.0.2
+  google_maps_flutter: ^2.2.1
+  google_maps_flutter_web: ^0.4.0+3
+  http: ^0.13.5
+  json_annotation: ^4.7.0
+  json_serializable: ^6.5.4
+dev_dependencies:
+  analysis_defaults:
+    path: ../analysis_defaults
+  flutter_test:
+    sdk: flutter
+  flutter_lints: ^2.0.0
+  build_runner: ^2.3.2
+flutter:
+  uses-material-design: true
+  assets:
+    - assets/locations.json