LibGUI: Make a macro for registering a GUI::Margins object property

This will allow anyone to register a margins property without having
to duplicate the parsing logic.

Userland/Libraries/LibGUI/Layout.cpp

@@ -14,26 +14,7 @@ namespace GUI {
 Layout::Layout()
 {
     REGISTER_INT_PROPERTY("spacing", spacing, set_spacing);
-
+    REGISTER_MARGINS_PROPERTY("margins", margins, set_margins);
-    register_property(
-        "margins",
-        [this] {
-            JsonObject margins_object;
-            margins_object.set("left", m_margins.left());
-            margins_object.set("right", m_margins.right());
-            margins_object.set("top", m_margins.top());
-            margins_object.set("bottom", m_margins.bottom());
-            return margins_object;
-        },
-        [this](auto value) {
-            if (!value.is_array() || value.as_array().size() != 4)
-                return false;
-            int m[4];
-            for (size_t i = 0; i < 4; ++i)
-                m[i] = value.as_array().at(i).to_i32();
-            set_margins({ m[0], m[1], m[2], m[3] });
-            return true;
-        });
 
     register_property("entries",
         [this] {

Userland/Libraries/LibGUI/Margins.h

@@ -46,4 +46,25 @@ private:
     int m_right { 0 };
     int m_bottom { 0 };
 };
+
 }
+
+#define REGISTER_MARGINS_PROPERTY(property_name, getter, setter)   \
+    register_property(                                             \
+        property_name, [this]() {                                  \
+            auto m = getter();                                     \
+            JsonObject margins_object;                             \
+            margins_object.set("left", m.left());                  \
+            margins_object.set("right", m.right());                \
+            margins_object.set("top", m.top());                    \
+            margins_object.set("bottom", m.bottom());              \
+            return margins_object; },                               \
+        [this](auto& value) {                                      \
+            if (!value.is_array() || value.as_array().size() != 4) \
+                return false;                                      \
+            int m[4];                                              \
+            for (size_t i = 0; i < 4; ++i)                         \
+                m[i] = value.as_array().at(i).to_i32();            \
+            setter({ m[0], m[1], m[2], m[3] });                    \
+            return true;                                           \
+        });