XPath: implement lang() and id() core functions #34593
Description
These are still missing from the XPath evaluator implementation. Relevant specs:
- https://www.w3.org/TR/1999/REC-xpath-19991116/#function-lang
- https://www.w3.org/TR/1999/REC-xpath-19991116/#function-id
Feature tracking issue at #34527