Shadergen types: Add Metal & MSL

include/PICA/shader_gen_types.hpp

@@ -2,8 +2,8 @@
 
 namespace PICA::ShaderGen {
 	// Graphics API this shader is targetting
-	enum class API { GL, GLES, Vulkan };
+	enum class API { GL, GLES, Vulkan, Metal };
 
-	// Shading language to use (Only GLSL for the time being)
+	// Shading language to use
-	enum class Language { GLSL };
+	enum class Language { GLSL, MSL };
-}  // namespace PICA::ShaderGen
+}  // namespace PICA::ShaderGen