Add SmartspaceView.setUiSurface and set it for lockscreen Smartspace.

Currently, we only need to set this for lockscreen Smartspace. When the
UI surface is set to "lockscreen", the date will update on Always-On
Display. See ag/20750544.

We can also deprecate the existing setIsDreaming method in favor of
setUiSurface. That's a separate issue and will be addressed separately.

Bug: 262046287
Test: manunal. Compared behavior and trace before/after the fix.
Test: atest LockscreenSmartspaceControllerTest.kt
Change-Id: I57126499dce033444d2c134f33a8b417e111ba65