Switch to namespace import, now that the types are no longer ambiguous

Terminal.Gui/Terminal.Gui.csproj

@@ -90,10 +90,7 @@
   <ItemGroup>
     <Using Include="JetBrains.Annotations" />
     <Using Include="System.Diagnostics.Contracts.PureAttribute" Alias="PureAttribute" />
-    <Using Include="System.Drawing.Rectangle" Alias="Rectangle" />
-    <Using Include="System.Drawing.RectangleF" Alias="RectangleF" />
-    <Using Include="System.Drawing.Point" Alias="Point" />
-    <Using Include="System.Drawing.PointF" Alias="PointF" />
+    <Using Include="System.Drawing" />
     <Using Include="System.Text" />
     <Using Include="JetBrains.Annotations" />
   </ItemGroup>

UnitTests/UnitTests.csproj

@@ -46,10 +46,7 @@
     </None>
   </ItemGroup>
   <ItemGroup>
-    <Using Include="System.Drawing.Rectangle" Alias="Rectangle" />
-    <Using Include="System.Drawing.RectangleF" Alias="RectangleF" />
-    <Using Include="System.Drawing.Point" Alias="Point" />
-    <Using Include="System.Drawing.PointF" Alias="PointF" />
+    <Using Include="System.Drawing" />
     <Using Include="Terminal.Gui" />
     <Using Include="Xunit" />
   </ItemGroup>