feat(flame): Add helper methods to create frame data on SpriteSheet (#2754)

Add two methods to SpriteSheet to create frame data for SpriteAnimation

doc/tutorials/klondike/step1.md

@@ -75,14 +75,14 @@ klondike/
  └─pubspec.yaml
 ```
 
-By the way, this kind of file is called the **spritesheet**: it's just a
+By the way, this kind of file is called the **sprite sheet**: it's just a
 collection of multiple independent images in a single file. We are using a
-spritesheet here for the simple reason that loading a single large image is
+sprite sheet here for the simple reason that loading a single large image is
 faster than many small images. In addition, rendering sprites that were
 extracted from a single source image can be faster too, since Flutter will
 optimize multiple such drawing commands into a single `drawAtlas` command.
 
-Here are the contents of my spritesheet:
+Here are the contents of my sprite sheet:
 
 - Numerals 2, 3, 4, ..., K, A. In theory, we could have rendered these in the
     game as text strings, but then we would need to also include a font as an

doc/tutorials/klondike/step2.md

@@ -39,9 +39,9 @@ have been more difficult to access that image from other classes.
 
 Also note that I am `await`ing the image to finish loading before initializing
 anything else in the game. This is for convenience: it means that by the time
-all other components are initialized, they can assume the spritesheet is already
+all other components are initialized, they can assume the sprite sheet is already
 loaded. We can even add a helper function to extract a sprite from the common
-spritesheet:
+sprite sheet:
 
 ```dart
 Sprite klondikeSprite(double x, double y, double width, double height) {
@@ -193,7 +193,7 @@ not planning to change these values during the game:
 Next, we will create a `Stock` component, the `Waste`, four `Foundation`s and
 seven `Pile`s, setting their sizes and positions in the world. The positions
 are calculated using simple arithmetics. This should all happen inside the
-`onLoad` method, after loading the spritesheet:
+`onLoad` method, after loading the sprite sheet:
 
 ```dart
     final stock = Stock()

doc/tutorials/klondike/step3.md

@@ -71,9 +71,9 @@ after the image is loaded into the cache.
 ```
 
 The last four numbers in the constructor are the coordinates of the sprite
-image within the spritesheet `klondike-sprites.png`. If you're wondering how I
+image within the sprite sheet `klondike-sprites.png`. If you're wondering how I
 obtained these numbers, the answer is that I used a free online service
-[spritecow.com] -- it's a handy tool for locating sprites within a spritesheet.
+[spritecow.com] -- it's a handy tool for locating sprites within a sprite sheet.
 
 Lastly, I have simple getters to determine the "color" of a suit. This will be
 needed later when we need to enforce the rule that cards can only be placed

doc/tutorials/platformer/step_1.md

@@ -52,10 +52,10 @@ provide free pixel art that can be used in games, but please check and comply wi
 always provide valid creator attribution.  For this game though, I am going to take a chance and
 make my artwork using an online pixel art tool.  If you decide to use this tool, multiple online
 tutorials will assist you with the basic operations as well as exporting the assets.  Now normally,
-most games will utilize spritesheets.  These combine many images into one larger image that can be
+most games will utilize sprite sheets.  These combine many images into one larger image that can be
 sectioned and used as individual images.  For this tutorial though, I specifically will save the
 images individually as I want to demonstrate the Flame engine's caching abilities.  Ember and the
-water enemy are spritesheets though as they contain multiple images to create animations.
+water enemy are sprite sheets though as they contain multiple images to create animations.
 
 Right-click the images below, choose "Save as...", and store them in the `assets/images` folder of the
 project. At this point our project's structure looks like this: