Fixes#97066
`RBSet` were used on `RotatedFileLogger` because it guarantees that
iterating it is done via `operator<`. This is important because
`RotatedFileLogger` depends on this behavior to delete the oldest log file.
On #61194 `HashSet` was added and all `RBSet` uses were replaced by
`HashSet`.
When that happened, the iteration in order is guaranteed to be the insertion
order, wich made that `RotatedFileLogger` delete the newest log file.
As a bonus, I added unit test for `RotatedFileLogger` and `CompositeLogger`.
d1338528f9