This commit adds the PSR-20 ClockInterface to core, with a
moodle-specific extension to the Interface at `\core\clock`, and a
standard clock at `\core\system_clock`.
Further clocks are provided as `\incrementing_clock` and `\frozen_clock`
which are available to unit tests using:
- `$this->mock_clock_with_incrementing(?int $starttime = null);`
- `$this->mock_clock_with_frozen(?int $time = null);`
For the incrementing clock, every call to fetch the time will bump the
current time by one second.
For the frozen clock the time will not change, but can be modified with:
- `$clock->set_to(int $time);`; and
- `$clock->bump(int $seconds = 1);`
The \core\di class is a Moodle wrapper to php-di which is intended to
allow Moodle to switch to an alternate DI solution in the future if
required. All interaction with the container uses the PSR-11 Container
interfaces, which allows for normalisation of configuration, setting,
and retrieving of DI container-identified classes.
Andrew Nicols