Vulkan: Retry instance creation if validation layer is not present

[ColinKinloch]

When running the flatpak if the vulkan validation layer is enabled Cemu crashes with an error box that says "Error when initializing Vulkan renderer: Unable to create a Vulkan instance: -6"

For some reason this goes away when running with the --devel option.

This MR adds a second attempt at creating a instance disabling all vulkan layers.

This is what Q2RTX does.

I initially tried checking against the list returned by vkEnumerateInstanceLayerProperties but it reports that VK_LAYER_KHRONOS_validation is present.

[Exzap]

It is by design that Cemu refuses to start with validation layer enabled but not present. Granted, we could display a better error message. But I believe that just silently ignoring the error will lead only to confusion on the users side, especially since the validation layer needs to be turned on explicitly.

[ColinKinloch]

The fact the debug options are in the menu bar rather than the settings also complicated debugging this.

[Exzap]

I'll merge this as-is and add error logging
ah nvm I'm blind. It's already there.