TV Placeholders: Update the assets

The assets used for the folders and medias placeholders could be updated to match the native appearance.

changed milestone to %3.5.0

added AppleTV Interface Maintenance labels

What is the native appearance for tvOS for files and folders?

This is what they look like for files for example:

It seems the placeholders are the same for both iOS and tvOS

I'm not sure we should adapt this style as we are listing files and folders, while Apple Music just lists media tracks with no such differentiation.

removed milestone %3.5.0

changed milestone to %4.0.0

added Feature label