[flexiglass] Update ScrollViewFields#intrinsicStackHeight on the LS

Update ScrollViewFields#intrinsicStackHeight to the restricted stack height,
when we are on the LockScreen. Stop using NSSL.mIntrinsicContentHeight,
when flexiglass is enabled.

Bug: 296118689
Test: atest NotificationStackScrollLayoutTest
Flag: com.android.systemui.scene_container
Change-Id: I7bd162f018e502ceb1d40ce9b48a644666b89fea