Phpstan Baseline Fixes 2022-09-21

[oleibman]

Eliminate about 200 more lines from Phpstan baseline. For Helper/Sample and Helper/Html and others, many properties are declared as protected despite the fact that the classes do not extend any other class, and there are no classes which extend them. They are changed to private; this could be a breaking change in circumstances for which I cannot think of a use case (user extends class for some reason).

This is:

- [x] a bugfix
- [ ] a new feature
- [ ] refactoring
- [ ] additional unit tests

Checklist:

• [x] Changes are covered by unit tests
  • [x] Changes are covered by existing unit tests
  • [x] New unit tests have been added
• [x] Code style is respected
• [x] 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
• [ ] Documentation is updated as necessary

Why this change is needed?

Provide an explanation of why this change is needed, with links to any Issues (if appropriate). If this is a bugfix or a new feature, and there are no existing Issues, then please also create an issue that will make it easier to track progress with this PR.