By separating them from unrelated code, their dependents
can use them without depending on unrelated code, which
in turn helps to reduce cyclic dependencies.
If the contained object type has a matches() method, CVariant::matches()
will call that method and return its result.
(This is a utility to allow using CVariant to represent an event subscription.)
This is an intermediate step to have smaller unit tests. It is a trade off
between having many many test executables compared to a few bigger ones. But
this comes a lot closer to what QtTest is meant to be used.
