[HSUM] Use SmartspaceManager in the current foreground user context.

For consistency, also switched to use `userTracker.userContext` when
building the SmartspaceConfig needed to create the SmartspaceSession.
However, that change has no effect on this bug - the context was used
just to set the `mPackageName` field in the SmartspaceConfig.

Note: after this fix, Smartspace **still** doesn't work correctly after
user switching. It keeps showing the features for the original user,
until the device is rebooted to the new user. However, Smartspace never
had support for user switching, so will handle that separately.

Flag: EXEMPT bugfix
Fix: 283290296
Fix: 362889846
Fix: 364377164
Test: check lockscreen smartspace cards on a device with HSUM.
Test: check lockscreen smartspace cards on a device w/o HSUM.
Test: check timer in Glanceable hub with and w/o HSUM.
Test: test the same thing after user switching with and w/o rebooting.
Test: LockscreenSmartspaceControllerTest
Change-Id: I817bb86fda901600abfad5881263d02793aa29fb