New OpenGL threading code - call for testing

[fivefeet8]

There seems to be a huge regression with Vulkan performance in a few games with the latest git builds. Earth Defense Force 2 is massively slower now with Vulkan. At the same time, OpenGL performance in this game has more than doubled. The game is now playable with OpenGL and complete unplayable with Vulkan. A complete vice versa from previous builds.

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I must say though, OpenGL in the latest builds have increased performance in some instances substantially. In some games, it's neck and neck with Vulkan.