fix: Adjust platformer tutorial steps (#2845)

This small PR adjusts:
1. some `backticks` (`) in the platformer tutorial in order to have a
proper highlight of the file names.
2. replaces backslash (`\`) with slash (`/`) in order to be consistent
with the other file paths used in the tutorial.
3. renames the variable `_xOffset` to `xOffset` in order to be
consistent with the rest of the code.

Co-authored-by: Rodrigo Castro <rodrigo.desouzacastro@bahag.com>

doc/tutorials/platformer/step_2.md

@@ -62,7 +62,7 @@ class EmberQuestGame extends FlameGame {
 As I mentioned in the [assets](step_1.md#assets) section, we are using multiple individual image
 files and for performance reasons, we should leverage Flame's built-in caching system which will
 only load the files once, but allow us to access them as many times as needed without an impact to
-the game. `await images.loadAll()` takes a list of the file names that are found in `assets\images`
+the game. `await images.loadAll()` takes a list of the file names that are found in `assets/images`
 and loads them to cache.
 
 

doc/tutorials/platformer/step_3.md

@@ -403,7 +403,7 @@ Now we just need to finish the `onLoad` method. So make your `onLoad` method loo
   void onLoad() {
     final platformImage = game.images.fromCache('block.png');
     sprite = Sprite(platformImage);
-    position = Vector2((gridPosition.x * size.x) + _xOffset,
+    position = Vector2((gridPosition.x * size.x) + xOffset,
         game.size.y - (gridPosition.y * size.y),
     );
     add(RectangleHitbox(collisionType: CollisionType.passive));

doc/tutorials/platformer/step_5.md

@@ -8,7 +8,7 @@ If you were waiting for some serious coding, this chapter is it. Prepare yoursel
 The first step will be to allow control of Ember via the keyboard. We need to start by adding the
 appropriate mixins to the game class and Ember. Add the following:
 
-`lib/ember_quest.dart'
+`lib/ember_quest.dart`
 
 ```dart
 import 'package:flame/events.dart';

doc/tutorials/platformer/step_6.md

@@ -149,7 +149,7 @@ class Hud extends PositionComponent with HasGameRef<EmberQuestGame> {
 In the `onLoad` method, you can see where we loop from 1 to the `game.health` amount, to create
 the number of hearts necessary. The last step is to add the hud to the game.
 
-Go to 'lib/ember_quest.dart` and add the following code in the `initializeGame` method:
+Go to `lib/ember_quest.dart` and add the following code in the `initializeGame` method:
 
 ```dart
 cameraComponent.viewport.add(Hud());