faec0638872798b58b9882ee079014555bc8393e log: Use Join() helper when listing log categories (MarcoFalke)
Pull request description:
This removes the global `ListLogCategories` and replaces it with a one-line member function `LogCategoriesString`, which just calls `Join`. Should be a straightforward refactor to get rid of a few LOC.
Backport of Core PR18669