DRM-specific messages and support link

[defagos]

One of our stories asked us to display a DRM-specific error message in Letterbox, letting the user access more information in Safari by tapping on a dedicated button.

This story was implemented but could not work because DRM errors are not correctly forwarded from the resource loader delegate to AVPlayer, and thus to SRGMediaPlayerController, because of an AVFoundation bug.

Once this issue has been fixed, and if this still makes sense, we can implement the desired message. What remains to be done:

• [ ] Rebase the feature/drm-external-link
• [ ] Make SRG Content Protection errors public, and add a type information to make a difference between Akamai and FairPlay issues.
• [ ] Update the existing SRGLetterboxErrorView implementation to only display errors for FairPlay.
• [ ] Check that the resource loader issue preventing correct UI behavior has been fixed, or find a proper workaround.

[defagos]

We probably weren't lucky when we first investigated this need, as having non-zero integer error codes in Objective-C, or integer non-zero enum values in Swift, allows the errors to be better propagated. Note that the error message itself seems to be correctly propagated since iOS 15, though the code is correctly propagated on iOS 14. I didn't test earlier versions.