Add basic support for `ang/*.test.php` test suite.

Add basic support for `ang/*.test.php` test suite.

The previous pattern was to put all tests in `tests/phpunit/`. They would use
fixtures in a few ways, eg

* Work with example forms from the `ang/` folder. This is useful for testing specific configurations/features
  (e.g. if a form is configured with `permission` of `X`, then the form should behave accordingly).
* Dynamically create/destroy forms. This is useful for testing the API mechanism (eg ensuring the `Afform.create`
  and `Afform.revert` actually do create and revert things).

The two styles are both necessary. However:

1. The first style is easer to work with -- if a form fails its test, then
   you can run that form interactively.  If you want to add a new test-case,
   you can simply copy in a working example -- you don't need to code-up
   some PHPUnit logic to build the example.

2. If you have something written in the first style, then it's easier keep
   the `*.aff.html` and the PHPUnit `*.php` next to each other.