Most notably:
* Use the much more narrow UserIdentity interface where possible.
* Make array type hints in PHPDocs as specific as possible.
Change-Id: Id189da4028b7874909277881dcf6539169dd13b6
Changes to the use statements done automatically via script
Addition of missing use statements done manually
Change-Id: Iad87245bf8082193be72f7e482f29e9f1bad11fc