Create test for CategoryManager.

- Move SettingsLibTests to tests/integ
- Create a new robotests directory for SettingsLib.
- Add test cases for CategoryManager#backwardCompatCleanupForCategory

Bug: 32382487
Test: make RunSettingsLibRoboTests
Change-Id: I7ef5921ce8c47a3e1e7209be1abc97ea549a2378