Convert ext/xsl to HNI.

Two new tests:
```zend/bad/ext/xsl/tests/bug53965.php``` failing because of missing entity loader (see https://github.com/facebook/hhvm/pull/2376)
```zend/good/ext/xsl/tests/xslt010.php``` passing, imported from php-src

Signed-off-by: Arthur Loiret <arthur.loiret@ens-lyon.fr>