AK+Everywhere: Convert JSON value serialization to String

This removes the use of StringBuilder::OutputType (which was ByteString,
and only used by the JSON classes). And it removes the StringBuilder
template parameter from the serialization methods; this was only ever
used with StringBuilder, so a template is pretty overkill here.

Libraries/LibIPC/Encoder.cpp

@@ -82,7 +82,7 @@ ErrorOr<void> encode(Encoder& encoder, ByteBuffer const& value)
 template<>
 ErrorOr<void> encode(Encoder& encoder, JsonValue const& value)
 {
-    return encoder.encode(value.serialized<StringBuilder>());
+    return encoder.encode(value.serialized());
 }
 
 template<>