Safely remove Wi-Fi user credentials

- Show "(In use)" if a credential is used by Wi-Fi networks

- Show Wi-Fi networks in use in the details dialog

- Disable "Uninstall" button if the credential is in use

Bug: 258542666
Test: manual test
atest -c UserCredentialsSettingsTest

Change-Id: I1fb29b58698d918f987b9a16c195127cf270c17e