[video_core] Properly disable/avoid building OpenGL when it's disabled (#3692)

- OpenGL symbols would still be included in builds without OpenGL, this pr fixes that
- Same goes for Vulkan, but now with `ENABLE_VULKAN`
- Add support to have OpenGL-only builds (why would you do this?)
- Add support for headless runs (yes you could just select NULL backend, but why not compile it headless? :)

Signed-off-by: lizzie <lizzie@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3692
Reviewed-by: crueter <crueter@eden-emu.dev>
Reviewed-by: DraVee <chimera@dravee.dev>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>

src/yuzu/vk_device_info.cpp

@@ -77,4 +77,5 @@ void PopulateRecords(std::vector<Record>& records, QWindow* window) try {
 } catch (const Vulkan::vk::Exception& exception) {
     LOG_ERROR(Frontend, "Failed to enumerate devices with error: {}", exception.what());
 }
+
 } // namespace VkDeviceInfo