make regex in controllermethodreflector.php compatible with PCRE 6.x

The syntax ?<...> seems to be only supported from PCRE 7.0 on. For
backwards-compability ?P<...> is used.
Merge pull request #12825 from d1saster/stable7-fixpcre

make regex in controllermethodreflector.php compatible with PCRE 6.x