These are currently implemented as members of Test, but they only manipulate a static singleton CaptureLogs object.

We should make these functions available as nonmember functions in mongo::unittest and change all callers to use the unittest:: qualified name.

The ~Test() destructor stops log capturing after a test finishes and is being destroyed. The same effect can be achieved through an RAII object usable by any test that wants to use it.

This is important for Gtest migration SPM-2926 as there, we aren't always using a base Test class that we control.