Codechange: Replace pointer to Sprite array with reference to SpriteCollection. (#11580)

Add `SpriteLoader::SpriteCollection` type which is an array of `SpriteLoad::Sprite`.

This removes the ambiguity of what `SpriteLoader::Sprite *` is pointing to,
and cleans up mismatches using both dereference -> and array access [] for the
same object.

src/blitter/32bpp_anim_sse4.hpp

@@ -39,7 +39,7 @@ public:
 	template <BlitterMode mode, Blitter_32bppSSE_Base::ReadMode read_mode, Blitter_32bppSSE_Base::BlockType bt_last, bool translucent, bool animated>
 	void Draw(const Blitter::BlitterParams *bp, ZoomLevel zoom);
 	void Draw(Blitter::BlitterParams *bp, BlitterMode mode, ZoomLevel zoom) override;
-	Sprite *Encode(const SpriteLoader::Sprite *sprite, AllocatorProc *allocator) override {
+	Sprite *Encode(const SpriteLoader::SpriteCollection &sprite, AllocatorProc *allocator) override {
 		return Blitter_32bppSSE_Base::Encode(sprite, allocator);
 	}
 	const char *GetName() override { return "32bpp-sse4-anim"; }