[Cleanup] Use explicit conversions for enum formatting (#4064)

This is prep for updating to fmt 10 which removed implicit conversions
for enums.

common/textures.h

@@ -54,6 +54,8 @@ namespace EQ
 			tintInvalid = textureInvalid
 		};
 
+		constexpr int format_as(TextureSlot slot) { return static_cast<int>(slot); }
+
 		const int8 LastTexture = weaponSecondary;
 		const int8 LastTintableTexture = tintFeet;