trunk/75eef9d8859933986ec75ce29aa4e472aefe0a4c: [BE][Ez]: Use rvalue overload for stringstream str (#186552)

«CPP20 introduced an rvalue overload to stringstream.str() . Without it, the string is copied out for the str() call every time. Now, we can steal the internal string buffer and return it directly through the rvalue overl...»