Plumbing for BravePlaylistExclusions component. Installer and registrar to follow suite Expose PlaylistExclusionsAPI as a protocol with a private impl so Swift can mock it, and add BravePlaylistExclusions.sharedInstance instead of exposing a wrapper on BraveCoreMain. Register the public header directly in ios/BUILD.gn and remove unused playlist deps from ios/app and ios/browser/web. Signed-off-by: Eli Hini <8249954+EliHini@users.noreply.github.com>