Share HTTP status codes map between SAPIs

There's some other stuff (header parsing etc.) which also ought to be shared, but this is, at least, a start.

This also means other code in PHP can benefit from this info.
@TazeTSchnitzel This condition can be omitted, because current shared map no longer contains code-text pair `{0, NULL}` as did previous map. According to this case, the `else`-block will never get run.