Phpstan Tweaks

[oleibman]

Phpstan level 10 reports an enormous number of errors. So does the excluded missingType.iterableValue. I do not plan to introduce either any time soon. But I will submit piecemeal changes from time to time. Changes will be mostly limited to phpdoc type declarations.

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests
• code quality

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• Documentation is updated as necessary