Move LogBuffer and related to SystemUILogLib.

This change
- creates a new logging library under /SystemUI/log/
- moves all classes under
  SystemUI/plugin/src/com/android/systemui/plugins/log/ into the new
  library

Test: verify LogBuffer works correctly on device
Test: atest LogBufferTest
Bug: 276475093
Change-Id: I0a963c660a288177be0f881312abffc84f95d5bf