* Reference docs for SL4J logging in Typed, #27648
* mention package implicit for LoggerOps
* reference docs of log testing utilities
* cleanup classic logging.md
* most of it is still relevant, and different enough from
typed/logging.md to keep it separate
* use ThresholdFilter instead of LevelFilter
Co-Authored-By: Will Sargent <will.sargent@gmail.com>
