Implemented cast devices selector on ash side

1, Created `MediaCastAudioSelectorView` on ash side which is a subclass
of the `global_media_controls::MediaItemUIDeviceSelector`
    - This view carries the cast list view and the audio list view
    - the audio list view will be added in a separate cl later

2, Created `MediaCastListView`.
    - Using the same device detecting logic as in the
`global_media_controls::MediaItemUIDeviceSelectorView`. It will only
detect the server casting devices, while in the cast detailed view
we detect the screen casting devices.
    - This class extends the `TrayDetailedView`, so that each cast
entry is in the same UI style as in the `CastDetailedView`

3, [browser/UI/ash] In the `MediaNotificationProviderImpl` returns
the ash cast device selector view if it's ash build and the
BackgroundListening flag is enabled.

4, [browser/UI/views] Refactored several helper functions to help
build the ash cast device selector view in #3.

5, Hide the separator line if it's ash build and BL flag is enabled
in the `global_media_controls::MediaItemUIDetailedView`


Bug: b/327507429
Change-Id: Ic699221e861addfa95ad3d248918f14eef80a3b0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5393298


Commit-Queue: Jiaming Cheng <jiamingc@chromium.org>
Reviewed-by: Andrew Xu <andrewxu@chromium.org>
Reviewed-by: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1282326}