Actual problems with these methods:
* Hiding class names in strings and relying on PHP's dark magic to turn strings into objects makes it hard to find usages of these classes.
* Abstract base classes for tests are considered evil. These patches are a step towards getting rid of the abstract base classes.
* It's just not necessary. Just override the `getInstance` method. Done. This is //sooo// much simpler.
`SerializerBaseTest::getClass` patches:
* https://gerrit.wikimedia.org/r/#/c/195295/ (merged)
* https://gerrit.wikimedia.org/r/#/c/195558/ (merged)
`ValueFormatterTestBase::getFormatterClass` base patch:
* Base: https://github.com/DataValues/Interfaces/pull/9 (merged) and https://github.com/DataValues/Interfaces/pull/10 (merged)
* https://github.com/DataValues/Common/pull/24 (merged)
* https://github.com/DataValues/Geo/pull/46 (merged)
* https://github.com/DataValues/Number/pull/28 (FAILS!)
* https://github.com/DataValues/Time/pull/46 (merged)
`ValueParserTestBase::getParserClass` patches:
* Base: https://github.com/DataValues/Common/pull/23 (merged) and https://github.com/DataValues/Common/pull/25 (merged)
* https://github.com/DataValues/Geo/pull/44 (merged)
* https://github.com/DataValues/Number/pull/26 (merged)
* https://github.com/DataValues/Time/pull/44 (merged)
* https://gerrit.wikimedia.org/r/#/c/194531/ (merged)