Build/Test Tools: Add support for PHPUnit 7.x.
- Create an abstract
WP_UnitTestCase_Base class to share between PHPUnit 7.x and older versions.
- Add a speed-trap loader to determine which
SpeedTrapListener class needs to be loaded for the current PHPUnit version.
- Remove unnecessary
PHPUnit\Util\Test and PHPUnit_Util_Getopt inheritances.
- Update Travis CI config to use PHPUnit 7.x for PHP 7.1, 7.2, and nightly PHP versions.
Props jipmoors, netweb, desrosj, ayeshrajans, soulseekah, SergeyBiryukov.
See #43218.