Using DI for all hook access means that it becomes significantly easier
to mock hooks and callbacks for unit testing without fundamentally
altering the structure of the code purely for the purposes of unit
testing.
In this commit, there are couple of fixes based on the report:
1. Removed legacy polyfill from provider.php
2. Fixed phpunit warning detected by CodeChecker
3. Removed unused files
4. Fixed the PHPunit failures by removing "securityquestions"
from the data_provider due to it has not been included as one of the factors
5. Added PHPunit test to the factors that can be unittested
6. Removed !important rule from tool_mfa/styles.css
7. Added (int) type to sleep method within sleep_timer method due to a php deprecation
in too_mfa/classes/manager.php
8. Changed last param form bool to string in not_enough_factors() when initiating
a new single_button object in tool_mfa/renderer.php
9. Add explanation text to login page
10. Fixed "Access to an undefined property .." from PHPStan
12. Fixed all the "Variable $.. might not be defined" from PHPStan
13. Fixed the issue from https://github.com/catalyst/moodle-tool_mfa/issues/379
Andrew Nicols