LibGfx: Move CIELAB to its own file

Userland/Libraries/LibGfx/CIELAB.h

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2023, Nico Weber <thakis@chromium.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+namespace Gfx {
+
+// https://en.wikipedia.org/wiki/CIELAB_color_space
+struct CIELAB {
+    float L; // L*
+    float a; // a*
+    float b; // b*
+};
+
+}