Persist ExposureWindow based risk level calculation results and update the UI (EXPOSUREAPP-3910,EXPOSUREAPP-3855) (#1705)

* First draft to refactor `RiskRepository` away and persist risk level results produced by ExposureWindow calculations.

TODO: Tests, Legacy data migration, Persist ExposureWindow's in tester builds.

* Unit tests for refactored classes.

* LINTs

* First draft for legacy risk data migration.

TODO: Tests.

* Store exposure windows on device for tester builds and perform clean on them too after risk result deletions.
Split RiskResultStorage such that the exposure window storage code is only available in deviceForTesters flavor builds.

* simplification

* no preference should return no value

* Remove TODOs, singletons are refactored away ;)

* Simplify RiskLevelTask interface

* Split risk level storage implementations to let production (device flavor) have a NOOP for storing/deleting exposure windows.

* Remove unused storage function.
Add test skeletons.

* unit test

* unit test

* Update risk card to show new window mode based information.

* Fix test regressions.

* Address PR comments.

* LINTs

* Everybody get's LINT for XMAS.

* Finish unit tests and remove unused classes.

Co-authored-by: chris-cwa <chris.cwa.sap@gmail.com>