Fix clang warning "mismatched-tags"

Change-Id: I00f26e27d8ac24a46b528ea7ed47b92c2967ff2e
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2390
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

MediaClientDefs: Cleanup unneded methods

MediaConnection: Review format negotiation mechanism

MediaClient: Reappropriate copyright

MediaClient: IDs should be signed integers

* It's very important to use a negative value to identify
non valid or uninitialized connections. Additionally, it's preferred
to don't interfere with media_kit types as long as the framework use
it in the backend.

MediaConnection: Implement auto release

MediaClient: Fix style for private methods and other cleanup

* Cleaned up some unneeded callbacks.

Populate media/experimental with future media_kit classes

* Node implementations headers are move into src/kits/media.