AK: Don't implicitly convert Optional<T&> to Optional<T>

C++ will jovially select the implicit conversion operator, even if it's
complete bogus, such as for unknown-size types or non-destructible
types. Therefore, all such conversions (which incur a copy) must
(unfortunately) be explicit so that non-copyable types continue to work.

NOTE: We make an exception for trivially copyable types, since they
are, well, trivially copyable.

Co-authored-by: kleines Filmröllchen <filmroellchen@serenityos.org>

Libraries/LibWeb/Fetch/Request.cpp

@@ -467,7 +467,7 @@ WebIDL::ExceptionOr<GC::Ref<Request>> Request::construct_impl(JS::Realm& realm,
     }
 
     // 38. Let inputOrInitBody be initBody if it is non-null; otherwise inputBody.
-    Optional<Infrastructure::Request::BodyType> input_or_init_body = init_body
+    Optional<Infrastructure::Request::BodyType const&> input_or_init_body = init_body
         ? Infrastructure::Request::BodyType { *init_body }
         : input_body;