ThemeEditor: Fix layout for new layout system

Userland/Applications/ThemeEditor/AlignmentProperty.gml

@@ -2,7 +2,7 @@
     layout: @GUI::HorizontalBoxLayout {
         spacing: 4
     }
-    shrink_to_fit: true
+    preferred_height: "fit"
 
     @GUI::Label {
         name: "name"

Userland/Applications/ThemeEditor/ColorProperty.gml

@@ -2,7 +2,7 @@
     layout: @GUI::HorizontalBoxLayout {
         spacing: 4
     }
-    shrink_to_fit: true
+    preferred_height: "fit"
 
     @GUI::Label {
         name: "name"

Userland/Applications/ThemeEditor/FlagProperty.gml

@@ -2,7 +2,7 @@
     layout: @GUI::HorizontalBoxLayout {
         spacing: 4
     }
-    shrink_to_fit: true
+    preferred_height: "fit"
 
     @GUI::CheckBox {
         name: "checkbox"

Userland/Applications/ThemeEditor/MainWidget.cpp

@@ -468,7 +468,7 @@ void MainWidget::add_property_tab(PropertyTab const& property_tab)
         group_box->layout()->set_spacing(12);
         // 1px less on the left makes the text line up with the group title.
         group_box->layout()->set_margins({ 8, 8, 8, 7 });
-        group_box->set_shrink_to_fit(true);
+        group_box->set_preferred_height(GUI::SpecialDimension::Fit);
 
         for (auto const& property : group.properties) {
             NonnullRefPtr<GUI::Widget> row_widget = group_box->add<GUI::Widget>();

Userland/Applications/ThemeEditor/MetricProperty.gml

@@ -2,7 +2,7 @@
     layout: @GUI::HorizontalBoxLayout {
         spacing: 4
     }
-    shrink_to_fit: true
+    preferred_height: "fit"
 
     @GUI::Label {
         name: "name"

Userland/Applications/ThemeEditor/PathProperty.gml

@@ -2,7 +2,7 @@
     layout: @GUI::HorizontalBoxLayout {
         spacing: 4
     }
-    shrink_to_fit: true
+    preferred_height: "fit"
 
     @GUI::Label {
         name: "name"