Add get_resource_id() function

> Hi internals, > > This originally came up in the "Stricter type-checks for > arithmetic/bitwise operators" thread. I would like to add a > get_resource_id() function, which does the same as an (int) $resource cast, > just in a more explicit way, that does not require the reader to be > familiar with PHP language minutiae. There is no plan to deprecate or > remove the (int) $resource form. > > This is similar to the recently added get_mangled_object_vars() function, > which is (about) the same as an (array) $object cast, but makes the > intention of working with mangled properties clearer clearer. > > The get_resource_id() name is based on the already existing > get_resource_type() function. > > The implementation is trivial and available at > https://github.com/php/php-src/pull/5427. >