Security fix for VPN app killable via lockscreen.

Do not show the active apps dialog when the screen is locked.
Instead prompt the user to unlock directly if clicked and only open the dialog on
successsful unlock.

Flag: NONE
Bug: 304772709
Test: manually, locked and unlocked
Test: atest com.android.systemui.qs.footer.ui.viewmodel.FooterActionsViewModelTest

(cherry picked from commit d7628d56)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:598d7a18601a04b9904f0e170cc7c1777a3389ff)
Merged-In: I384699d478e5abcee3a165afc45211b9ed96334a
Change-Id: I384699d478e5abcee3a165afc45211b9ed96334a