Codechange: Make SpriteType, CargoSortType, SourceType and ScriptType enum classes. (#10663)

This avoids a (soft) namespace conflict between the four ST_* enums.

src/gfx_type.h

@@ -305,12 +305,12 @@ enum PaletteType {
 };
 
 /** Types of sprites that might be loaded */
-enum SpriteType : byte {
-	ST_NORMAL   = 0,      ///< The most basic (normal) sprite
-	ST_MAPGEN   = 1,      ///< Special sprite for the map generator
-	ST_FONT     = 2,      ///< A sprite used for fonts
-	ST_RECOLOUR = 3,      ///< Recolour sprite
-	ST_INVALID  = 4,      ///< Pseudosprite or other unusable sprite, used only internally
+enum class SpriteType : byte {
+	Normal   = 0,      ///< The most basic (normal) sprite
+	MapGen   = 1,      ///< Special sprite for the map generator
+	Font     = 2,      ///< A sprite used for fonts
+	Recolour = 3,      ///< Recolour sprite
+	Invalid  = 4,      ///< Pseudosprite or other unusable sprite, used only internally
 };
 
 /**