This deprecates --vmodule (not available in absl, mapping it to --v for
a very minimal sort of compatibility) and adds the absl::log flags
--minloglevel, --stderrthreshold, --log_backtrace_at, and --log_prefix.
Related to issue #1047
After this it should be possible to build a working `packager` application from the `cmake` branch. Some further logging improvements may be needed to get full parity with the `main` branch in terms of ability to do verbose debug logging, but other than that everything is expected to work.
Joey Parrish
Cosmin Stejerean
KongQun Yang