Phpstan 10 and IterableValue Prep Part 2

[oleibman]

There will probably be dozens, if not hundreds, of these before I'm ready to commit.

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

[oleibman]

Scrutinizer "failure condition" is a false positive, and is now suppressed.