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
DOMComment::__construct() with constructor called twice.
DOMDocumentFragment::appendXML() with unbound fragment.
DOMDocumentFragment::appendXML() with unbalanced chunks.
DOMDocumentFragment::__construct() called twice.
DOMDocumentType: basic access to all properties.
DOMDocumentType::name with invalid state.
DOMDocumentType::entities with invalid state.
DOMDocumentType::notations with invalid state.
DOMDocumentType::publicId with invalid state.
DOMDocumentType::publicId with empty value.
DOMDocumentType::systemId with invalid state.
DOMDocumentType::systemId with empty value.
DOMDocumentType::internalSubset with invalid state.
