Fix end area button alignment and background for selected device.

- Use LinearLayout instead of FrameLayout and remove the calculated
margins to fix the end area button alignment.
- For a device that is in the dynamic group, fix the checkbox
background color.

Flag: EXEMPT bugfix
Bug: 393623732
Test: atest SystemUIGoogleRoboRNGTests:MediaOutputAdapterScreenshotTest,
    atest SystemUiRoboTests:MediaOutputAdapterTest
    atest SystemUiRoboTests:MediaSwitchingControllerTest
Change-Id: I24b6fa16670801a801fc8224db90059d3ac9a7be