refactor: Move shader classes (endless-sky#10385)

Author: tibetiroka

source/AlertLabel.cpp

@@ -17,9 +17,9 @@ this program. If not, see <https://www.gnu.org/licenses/>.
 
 #include "Angle.h"
 #include "GameData.h"
-#include "PointerShader.h"
+#include "shader/PointerShader.h"
 #include "Projectile.h"
-#include "RingShader.h"
+#include "shader/RingShader.h"
 #include "Ship.h"
 
 #include <algorithm>

source/AmmoDisplay.cpp

@@ -27,7 +27,7 @@ this program. If not, see <https://www.gnu.org/licenses/>.
 #include "Ship.h"
 #include "image/Sprite.h"
 #include "image/SpriteSet.h"
-#include "SpriteShader.h"
+#include "shader/SpriteShader.h"
 
 using namespace std;