Adding vsix signing. (#12758)

Build/signing/SignVsix.proj

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project DefaultTargets="SignFiles" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="packages\Microsoft.VisualStudioEng.MicroBuild.Core.0.4.1\build\Microsoft.VisualStudioEng.MicroBuild.Core.props" />
+
+  <PropertyGroup>
+    <BaseOutputDirectory>$(BUILD_STAGINGDIRECTORY)</BaseOutputDirectory>
+    <!-- These properties are required by MicroBuild, which only signs files that are under these paths -->
+    <IntermediateOutputPath>$(BaseOutputDirectory)</IntermediateOutputPath>
+    <OutDir>$(BaseOutputDirectory)</OutDir>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <FilesToSign Include="$(OutDir)\vsix\cpptools-*.signature.p7s">
+      <Authenticode>VSCodePublisher</Authenticode>
+    </FilesToSign>
+  </ItemGroup>
+
+  <Import Project="packages\Microsoft.VisualStudioEng.MicroBuild.Core.0.4.1\build\Microsoft.VisualStudioEng.MicroBuild.Core.targets" />
+</Project>