[flexiglass] Respect FoldGracePeriodProvider when showing dismissible LS

TSIA

Bug: 341445974
Test: manually verified that the feature falls back to just shutting off
the display if the for-eng system prop is turned off with adb shell setprop persist.fold_grace_period_enabled false && adb reboot
Test: manually verified that the feature still works if the system prop
is set to true
Flag: com.android.systemui.scene_container

Change-Id: Ia3157bca6d5152641d5024155cc5d8c08918787c