Add dimensions for notification channel panel

    Removes dependency on output switcher dimens.
    Fix notification settings bottom sheet scroll in landscape.

Test: adb shell cmd notification post "Test notif" &
    adb shell am start -a android.settings.CHANNEL_NOTIFICATION_SETTINGS     --es android.provider.extra.CHANNEL_FILTER_LIST "sound"     --es android.provider.extra.CHANNEL_ID "shell_cmd"     --es android.provider.extra.APP_PACKAGE "com.android.shell"

Bug: 238845213
Change-Id: Iaf4b52b0aa8376c93ebc55fc005cdb55d2a9620e