libobs: Prevent D3D11 projectors from tearing

Some users stream projectors, so don't let them tear. Use the waitable
object to check the flip queue, and only flip if there's space.

Metal and Vulkan can probably perform similar flip throttling once OBS
starts using them.
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f