LibWeb/CSS: Serialize short version if possible for "place-" properties

Output short version when both parts of place-content, place-items,
place-self are the same.

Author: kalenikaliaksandr

Userland/Libraries/LibWeb/CSS/StyleValues/PlaceContentStyleValue.cpp

@@ -10,7 +10,11 @@ namespace Web::CSS {
 
 ErrorOr<String> PlaceContentStyleValue::to_string() const
 {
-    return String::formatted("{} {}", TRY(m_properties.align_content->to_string()), TRY(m_properties.justify_content->to_string()));
+    auto align_content = TRY(m_properties.align_content->to_string());
+    auto justify_content = TRY(m_properties.justify_content->to_string());
+    if (align_content == justify_content)
+        return String::formatted("{}", align_content);
+    return String::formatted("{} {}", align_content, justify_content);
 }
 
 }

Userland/Libraries/LibWeb/CSS/StyleValues/PlaceItemsStyleValue.cpp

@@ -10,7 +10,11 @@ namespace Web::CSS {
 
 ErrorOr<String> PlaceItemsStyleValue::to_string() const
 {
-    return String::formatted("{} {}", TRY(m_properties.align_items->to_string()), TRY(m_properties.justify_items->to_string()));
+    auto align_items = TRY(m_properties.align_items->to_string());
+    auto justify_items = TRY(m_properties.justify_items->to_string());
+    if (align_items == justify_items)
+        return String::formatted("{}", align_items);
+    return String::formatted("{} {}", align_items, justify_items);
 }
 
 }

Userland/Libraries/LibWeb/CSS/StyleValues/PlaceSelfStyleValue.cpp

@@ -10,7 +10,11 @@ namespace Web::CSS {
 
 ErrorOr<String> PlaceSelfStyleValue::to_string() const
 {
-    return String::formatted("{} {}", TRY(m_properties.align_self->to_string()), TRY(m_properties.justify_self->to_string()));
+    auto align_self = TRY(m_properties.align_self->to_string());
+    auto justify_self = TRY(m_properties.justify_self->to_string());
+    if (align_self == justify_self)
+        return String::formatted("{}", align_self);
+    return String::formatted("{} {}", align_self, justify_self);
 }
 
 }