According to https://www.php.net/manual/en/class.domdocument:
When using json_encode() on a DOMDocument object the result will be
that of encoding an empty object.
But this was broken in 8.1. The output was `{"config": null}`.
That's because the config property is defined with a default value of
NULL, hence it was included. The other properties are not included
because they don't have a default property, and nothing is ever written
to their backing field. Hence, the JSON encoder excludes them.
Similarly, `(array) $doc` would yield the same `config` key in the
array.
Closes GH-11840.
At one point this was changed from a bool to an int in libxml2, with
negative values meaning it is unspecified. Because it is cast to a bool
this therefore returned true instead of the expected false.
Closes GH-11793.
For rationale, see https://github.com/php/php-src/pull/6787
Make extension checks lowercase, add a special case for opcache
that has internal name not matching .so filename.
Extensions migrated in part 2:
* dom
* exif
* fileinfo
* ffi
