The logger and logv2 namespaces have separate but identical implementations of LogSeverity, LogComponent, and LogComponentSettings. This causes pain in logv2 upgrades because we have to cast back and forth and it's unclear whether the namespaces are significant (they aren't).

Move the tests for these types into the logv2/ directory. After doing so, there are no more relevant logger/log_test.cpp tests, so a number of logger files can be eliminated and we won't have to maintain them anymore.