refactor: move player related sub-views to its own binding

[Bnyro]

Motivation:

• We previously duplicated the code to embed the views that are required by the player (e.g. the +10 seek indicator, autoplay countdown, ...) by pasting them everywhere a PlayerView instead is defined in XML
• This way is much cleaner and removes the duplicated code
• The changes also allow us to have more control over the ExoPlayer views inbuild components and use view bindings on it, which hasn't been possible before this PR.

Caveats:

• However, we unfortunately need to create a wrapper custom_exo_player_view around the real views, because PlayerView replaces @id/exo_controller_placeholder with the actual controller view in its constructor, so there's no way that we can prevent that behavior. That causes custom_exo_player_view not to be inflatable, because the view with id @id/exo_controller_placeholder doesn't exist anymore.
• We have to set the dimmed player controls background manually, because it would otherwise overlap the stuff behind it (i.e. the skip buttons)