Update CMake config with find_dependency

.nuget/DirectXTK12-config.cmake.in

@@ -1,5 +1,11 @@
 @PACKAGE_INIT@
 
 include(${CMAKE_CURRENT_LIST_DIR}/@PROJECT_NAME@-targets.cmake)
+include(CMakeFindDependencyMacro)
+
+if(VCPKG_TOOLCHAIN)
+    find_dependency(directx-headers CONFIG)
+    find_dependency(directxmath CONFIG)
+endif()
 
 check_required_components("@PROJECT_NAME@")