Adding UserAwareSecureSettingsRepository

Extracting part of StickyKeysRepositoryImpl into reusable UserAwareSecureSettingsRepository.

Why new class?
- existing SecureSettingsRepository is in shared customization module because it's used by WallpaperPicker. It cannot be moved out of it so WallpaperPicker can still use it and it can't be modified because it doesn't have dependency on core sysui module that includes SecureSettings and UserRepository

Why not using SecureSettingsRepository inside UserAwareSecureSettingsRepository?
- because it's dependent on ContentResolver which makes user-dependency less explicit - user is just taken from associated context. In theory it could be implemented with UserTracker.userContentResolver but that requires more callbacks and seems less explicit about what's going on.

Bug: 319837892
Test: UserAwareSecureSettingsRepositoryTest
Flag: N/A
Change-Id: I29114ad561ae997998a984c6d91d2bb90af7148f