New fix for bug #78263. This is special-cased elsewhere in the engine,
so we need to mirror it here.

This reverts commit 428cfdd1810b17f0064b7691276f0eb92dc963b6.

And remove the Reflector::export() interface method.

export() methods were implemented in a roundabout way, where they
would call Reflection::export(), which would then call __toString().
Cut out the middleman by directly calling __toString().

And don't return null for rc=1 references. Leave it to the user
to decide whether or not they want to consider these as references
or not.

Fixes bug #78263.

We weren't able to do this in 7.1 because the deprecation notice
may be converted to an exception and __toString() can't throw,
which means that it ultimately become a fatal error. This issue
is resolved now, so we can mark the method as deprecated.

RFC: https://wiki.php.net/rfc/tostring_exceptions

And convert some object to string conversion related recoverable
fatal errors into Error exceptions.

Improve exception safety of internal code performing string
conversions.