[TF2] [x64_test] tf_linux64: Fall back to OpenGL (toGL) if Vulkan (DXVK) fails.

[ChampionCynthia]

Hello,

Currently, when starting the x64 beta on a Linux system where Vulkan initialization fails, the game crashes.

By default, the new Beta ditches the legacy OpenGL "toGL" system for the more modern Vulkan "DXVK" system on Linux.

The game uses DXVK 2.X, which requires hardware with a Vulkan 1.3 compatible driver.

If the user's configuration lacks a Vulkan 1.3 compatible driver, DXVK 2 fails and the game fails to start. However, passing -gl as a command-line option forces the game to use toGL, allowing the game to run.

Thus, the game should:

• At best, fall back to toGL if DXVK cannot initialize.
• At worst, display a message box telling the user to add the -gl parameter.

I suspect this issue to cause another round of "game startup issues" after #5491.

It should be noted that this doesn't affect Windows currently since it is still configured to use DirectX 9 by default instead of DXVK. However, should DXVK be made the default on Windows as well, this issue will happen there too.

Cheers.