Provide ClipboardManager as a UserScopedService.

In HSUM we were getting the wrong ClipboardManager.

This does not fix:
- HSUM clipboard overlay (the UI still doesn't appear)
- Secondary users (we still don't listen for user switches)

Bug: 360415942
Test: Manual test with logs
Test: atest ClipboardListenerTest
Flag: EXEMPT bugfix.
Change-Id: Ib9759d48584ea653c6d674e82bad4791692c91ae