decklink: Update SDK to 12.8

[DDRBoxman]

Description

Update the Blackmagic SDK to 12.8

Motivation and Context

We were on SDK 11.6 and while we don't need any of the new APIs yet it's always nice to update dependencies.

How Has This Been Tested?

Compiled and run locally with the UltraStudio 4K Mini

Types of changes

• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[RytoEX]

Does it make sense to move these to obs-deps at some point? Or must these be hosted in-tree because that's the only way we can get them for Linux?

[DDRBoxman]

As far as I know you have to grab them from their website, I did not see an sdk package for Ubuntu

[RytoEX]

As far as I know you have to grab them from their website, I did not see an sdk package for Ubuntu

Unfortunate. Okay then.

[RytoEX]

Putting this in Draft in favor of #10513.