* a11y: remove SemanticsSortOrder; sort locally only; semanticsOwner post-test check
* update accessibility test framework
- default nextNodeId/previousNodeId to -1
- stop treating null as opt-out from value testing
- add `id`, `TestSemantics.root`, and `tags` to the suggested code in the TestSemantics failure message
- fix a small bug with raw string escaping
- update all tests accordingly
* fix sortKey doc
* prefer const over final