(split from main repo) Move common references into Directory.Build.props

* System
* System.ComponentModel.Composition
* System.Drawing
* System.Windows.Forms
* netstandard

Author: RussKie

GerritTests.csproj

@@ -7,11 +7,6 @@
     <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
   </PropertyGroup>
 
-  <ItemGroup>
-    <Reference Include="System" />
-    <Reference Include="System.Windows.Forms" />
-  </ItemGroup>
-
   <ItemGroup>
     <PackageReference Include="FluentAssertions" Version="5.2.0" />
     <PackageReference Include="NUnit" Version="3.10.1" />