Minor adjustements on UserManager.isUserForeground().

- Uses context user id instead of calling user id.
- Annotated with @UserHandleAware.
- Updated javadoc.

Test: m update-apis
Test: atest CtsMultiUserTestCases
Bug: 173541467

Change-Id: Id61fb73f2b7313265554cff9f496eb118a7e6a1e
3 files changed