LibWeb: Remove StringBuilders from HTMLToken::m_doctype

Author: https://github.com/gunnarbeutner
Commit: 992964aa7d
Pull-request: https://github.com/SerenityOS/serenity/pull/8687
Reviewed-by: https://github.com/alimpfard

Userland/Libraries/LibWeb/HTML/Parser/HTMLToken.h

@@ -194,11 +194,11 @@ private:
     struct {
         // NOTE: "Missing" is a distinct state from the empty string.
 
-        StringBuilder name;
+        String name;
         bool missing_name { true };
-        StringBuilder public_identifier;
+        String public_identifier;
         bool missing_public_identifier { true };
-        StringBuilder system_identifier;
+        String system_identifier;
         bool missing_system_identifier { true };
         bool force_quirks { false };
     } m_doctype;