Fix orphans check
Fix orphans check

This effectively forbids line breaks before the first line. Also, check
the orphans property on the block parent, as it only applies to block container
elements per spec.

Based on work in #1356
Fixes #1617

Co-authored-by: David Sickmiller <aa743a0aaec8f7d7a1f01442503957f4d7a2d634@sickmiller.com>

dompdf/dompdf,dompdf/dompdf