This seems to be a simple oversight, where we did not enable
exceptions. Other constexpr conditions already throw, so there is
no particular reason to stick to a fatal error here.

In PHP static properties are shared between inheriting classes,
unless they are explicitly overwritten. However, because this
functionality was implemented using reference, it was possible
to break the implementation by reassigning the static property
reference.

This is fixed by switching the implementation from using references
to using INDIRECTs, which cannot be affected by userland code.

EXPECTF logic in run-tests.php is considerable, so let's avoid it.

PHP requires integer typehints to be written "int" and does not
allow "integer" as an alias. This changes type error messages to
match the actual type name and avoids confusing messages like
"must be of the type integer, integer given".

As the parent class is fetched prior to binding, there are no
safety concerns in this case and we can replace the fatal error
with an Error exception.

RFC: https://wiki.php.net/rfc/object-typehint