LibWeb: Make the CSS serialization functions actually output things :^)

Pro tip: If your function takes a StringBuilder by value, it doesn't
actually append anything to the caller's StringBuilder. On the plus
side, I probably won't make this mistake for a while? I hope?

Userland/Libraries/LibWeb/CSS/Serialize.cpp

@@ -11,20 +11,20 @@
 namespace Web::CSS {
 
 // https://www.w3.org/TR/cssom-1/#escape-a-character
-void escape_a_character(StringBuilder builder, u32 character)
+void escape_a_character(StringBuilder& builder, u32 character)
 {
     builder.append('\\');
     builder.append_code_point(character);
 }
 
 // https://www.w3.org/TR/cssom-1/#escape-a-character-as-code-point
-void escape_a_character_as_code_point(StringBuilder builder, u32 character)
+void escape_a_character_as_code_point(StringBuilder& builder, u32 character)
 {
     builder.appendff("\\{:x} ", character);
 }
 
 // https://www.w3.org/TR/cssom-1/#serialize-an-identifier
-void serialize_an_identifier(StringBuilder builder, StringView const& ident)
+void serialize_an_identifier(StringBuilder& builder, StringView const& ident)
 {
     Utf8View characters { ident };
     auto first_character = characters.is_empty() ? 0 : *characters.begin();
@@ -76,7 +76,7 @@ void serialize_an_identifier(StringBuilder builder, StringView const& ident)
 }
 
 // https://www.w3.org/TR/cssom-1/#serialize-a-string
-void serialize_a_string(StringBuilder builder, StringView const& string)
+void serialize_a_string(StringBuilder& builder, StringView const& string)
 {
     Utf8View characters { string };
 
@@ -108,7 +108,7 @@ void serialize_a_string(StringBuilder builder, StringView const& string)
 }
 
 // https://www.w3.org/TR/cssom-1/#serialize-a-url
-void serialize_a_url(StringBuilder builder, StringView const& url)
+void serialize_a_url(StringBuilder& builder, StringView const& url)
 {
     // To serialize a URL means to create a string represented by "url(",
     // followed by the serialization of the URL as a string, followed by ")".

Userland/Libraries/LibWeb/CSS/Serialize.h

@@ -12,11 +12,11 @@
 
 namespace Web::CSS {
 
-void escape_a_character(StringBuilder, u32 character);
-void escape_a_character_as_code_point(StringBuilder, u32 character);
-void serialize_an_identifier(StringBuilder, StringView const& ident);
-void serialize_a_string(StringBuilder, StringView const& string);
-void serialize_a_url(StringBuilder, StringView const& url);
+void escape_a_character(StringBuilder&, u32 character);
+void escape_a_character_as_code_point(StringBuilder&, u32 character);
+void serialize_an_identifier(StringBuilder&, StringView const& ident);
+void serialize_a_string(StringBuilder&, StringView const& string);
+void serialize_a_url(StringBuilder&, StringView const& url);
 
 String escape_a_character(u32 character);
 String escape_a_character_as_code_point(u32 character);