vcpkg: Enable vulkan feature for sdl2

The comp_window_peek needs sdl2 with Vulkan supporting, and normal sdl2
installation doesn't support Vulkan. So we need to install Vulkan
feature of sdl2 explicitly to let sdl2 work with Vulkan, and let
comp_window_peek works on Windows.

vcpkg.json

@@ -35,7 +35,13 @@
         "gui": {
             "description": "Debug GUI support",
             "dependencies": [
-                "sdl2"
+                {
+                    "name": "sdl2",
+                    "features": [
+                        "base",
+                        "vulkan"
+                    ]
+                }
             ]
         }
     }