Add generic LOG() macro with level parameter

One log macro was provided for each log level (LOGV(), LOGD(), LOGI(),
LOGW(), LOGE()).

Add a generic macro LOG(LEVEL, ...) accepting a log level as parameter,
so that it is possible to write logging wrappers.

PR #3005 <https://github.com/Genymobile/scrcpy/pull/3005>