Prevent making unnecessary requestDeviceSuggestion() calls.

This CL adds additional checks inside the scroll handler and triggers
panel's `onPanelFullyVisible` event when the panel becomes fully
visible and was not visible before.

To sum it up, make a `requestDeviceSuggestion()` call only when:
- The Media Controls carousel becomes visible.
- The card within the carousel becomes fully visible.

Fix: 434295012
Test: atest MediaCarouselControllerTest MediaCarouselScrollHandlerTest
Test: On a physical device
Flag: com.android.systemui.enable_suggested_device_ui
Change-Id: I49408eee27e0314b8b0260c935ee7444902b8c25