add vcpkg.json, and modify ci.yaml to improve usage vcpkg

Now we utilise storing dependencies in `vcpkg.json`, we can use this to
more easily install the dependencies.
Furthermore, we moved cloning vcpkg to `checkout`, which creates clones
with `--depth=1` by default.

.gitignore

@@ -19,4 +19,5 @@
 /test/bin/
 /test/obj/
 *.lock
+/vcpkg_installed/
 compile_commands.json