chore: refactor FullMapPage in example with FAB.

* add _nullIsland
* add canInteractWithMap bool to showcase waiting for onStyleLoadedCallback

Author: smallTrogdor

example/lib/full_map.dart

@@ -1,11 +1,14 @@
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 import 'package:maplibre_gl/maplibre_gl.dart';
 
 import 'page.dart';
 
+const _nullIsland = CameraPosition(target: LatLng(0, 0), zoom: 4.0);
+
 class FullMapPage extends ExamplePage {
-  const FullMapPage({super.key})
-      : super(const Icon(Icons.map), 'Full screen map');
+  const FullMapPage({super.key}) : super(const Icon(Icons.map), 'Full screen map');
 
   @override
   Widget build(BuildContext context) {
@@ -21,41 +24,28 @@ class FullMap extends StatefulWidget {
 }
 
 class FullMapState extends State<FullMap> {
-  MapLibreMapController? mapController;
-  var isLight = true;
-
-  _onMapCreated(MapLibreMapController controller) {
-    mapController = controller;
-  }
-
-  _onStyleLoadedCallback() {
-    ScaffoldMessenger.of(context).showSnackBar(
-      SnackBar(
-        content: const Text("Style loaded :)"),
-        backgroundColor: Theme.of(context).primaryColor,
-        duration: const Duration(seconds: 1),
-      ),
-    );
-  }
+  final Completer<MapLibreMapController> mapController = Completer();
+  bool canInteractWithMap = false;
 
   @override
   Widget build(BuildContext context) {
     return Scaffold(
-        // TODO: commented out when cherry-picking https://github.com/flutter-mapbox-gl/maps/pull/775
-        // needs different dark and light styles in this repo
-        // floatingActionButton: Padding(
-        // padding: const EdgeInsets.all(32.0),
-        // child: FloatingActionButton(
-        // child: Icon(Icons.swap_horiz),
-        // onPressed: () => setState(
-        // () => isLight = !isLight,
-        // ),
-        // ),
-        // ),
-        body: MapLibreMap(
-      onMapCreated: _onMapCreated,
-      initialCameraPosition: const CameraPosition(target: LatLng(0.0, 0.0)),
-      onStyleLoadedCallback: _onStyleLoadedCallback,
-    ));
+      floatingActionButtonLocation: FloatingActionButtonLocation.miniCenterFloat,
+      floatingActionButton: canInteractWithMap
+          ? FloatingActionButton(
+        onPressed: _moveCameraToNullIsland,
+        mini: true,
+        child: const Icon(Icons.restore),
+      )
+          : null,
+      body: MapLibreMap(
+        onMapCreated: (controller) => mapController.complete(controller),
+        initialCameraPosition: _nullIsland,
+        onStyleLoadedCallback: () => setState(() => canInteractWithMap = true),
+      ),
+    );
   }
+
+  void _moveCameraToNullIsland() =>
+      mapController.future.then((c) => c.animateCamera(CameraUpdate.newCameraPosition(_nullIsland)));
 }