Make UndockedRegFreeWinRT use same vcpkg_installed directory

Author: florelis

src/vcpkg.props

@@ -2,7 +2,7 @@
 <Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup Label="Vcpkg">
     <VcpkgEnableManifest>true</VcpkgEnableManifest>
-    <VcpkgInstalledDir>$(ProjectDir)..\vcpkg_installed</VcpkgInstalledDir>
+    <VcpkgInstalledDir>$(MSBuildThisFileDirectory)\vcpkg_installed</VcpkgInstalledDir>
   </PropertyGroup>
   <PropertyGroup Label="Vcpkg" Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
     <VcpkgTriplet>x64</VcpkgTriplet>