Add a contrast dot to the slider end.

Additionally, fix the scaling of the end area icon.

Flag: EXEMPT bugfix
Bug: 379967988
Fix: 379967988
Test: atest
    SystemUIGoogleScreenshotTests:MediaOutputAdapterScreenshotTest,
    On a physical device.
Change-Id: I9ad1d923678cbba2e94ee62e03f333d9a41a771d