Merge pull request dotnet/corefx#8932 from jcouv/deconstruction

ValueTuple: adding Deconstruct and other tuple interop methods for System.Tuple

Commit migrated from https://github.com/dotnet/corefx/commit/8886480f82b83d31a3d406ba711661d1937193f5

src/libraries/System.ValueTuple/src/System.ValueTuple.csproj

@@ -17,6 +17,7 @@
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="System\Runtime\CompilerServices\TupleElementNamesAttribute.cs" />
+    <Compile Include="System\ValueTuple\TupleExtensions.cs" />
     <Compile Include="System\ValueTuple\ValueTuple.cs" />
   </ItemGroup>
   <ItemGroup>

src/libraries/System.ValueTuple/tests/System.ValueTuple.Tests.csproj

@@ -10,6 +10,7 @@
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="TupleElementNamesAttribute\UnitTests.cs" />
+    <Compile Include="ValueTuple\ExtensionsTests.cs" />
     <Compile Include="ValueTuple\UnitTests.cs" />
   </ItemGroup>
   <ItemGroup>