[bc25] Fix notifications not being rendered on Dual Shade.

The bug was caused due to a recent change in NSSL that
requires positioning a `NotificationStackCutoffGuideline`
composable which communicates the bottom rendering boundary
to the NSSL.

Bug: 340553529
Bug: 348641274
Test: Manually verified on a device by opening and closing the
notifications dual shade.
Test: Existing unit tests still pass.
Flag: com.android.systemui.dual_shade

Change-Id: I03cc302c2f89f14e6a8724f49cfb93fb4eab3b16