[flexiglass] Fix QuickQSPanelControllerTest failures with SceneContainerFlag

Updated the `setUp` method in QuickQSPanelControllerTest to
conditionally mock dependencies
(`mediaCarouselInteractor.hasActiveMedia`,
`quickQSPanel.viewTreeObserver`, `mockViewTreeObserver.isAlive`,
`quickQSPanel.isAttachedToWindow`) only when SceneContainerFlag
is enabled. This resolves the initialization crashes.

Added `@DisableSceneContainer` annotation to the
`mediaExpansion_...` tests to ensure they only run when the
flag is disabled, as they test legacy behavior.

Bug: 416716468
Flag: com.android.systemui.scene_container
Test: com.android.systemui.qs.QuickQSPanelControllerTest
     Locally run this test and verify all the tests are passed with the
     `@EnableSceneContainer` annotation.
Change-Id: I8bb191b327338438bc1e3f6838181350e350d07a