[create-vsix] Copy Xamarin.Android.Sdk.json to output dir (#752)

Some internal workflows require the `Xamarin.Android.Sdk.json` file in
order to use the generated `.vsix`.

Copy the generated `Xamarin.Android.Sdk.json` file into the
directory that `$(VsixPath)` uses

Author: jonpryor

build-tools/create-vsix/create-vsix.targets

@@ -110,6 +110,7 @@
     </PropertyGroup>
     <PropertyGroup>
       <VsixPath Condition=" '$(VsixPath)' == '' ">..\..\bin\Build$(Configuration)\$(AssemblyName)-OSS-$(ProductVersion).$(XAVersionCommitCount)_$(_Branch)_$(XAVersionHash).vsix</VsixPath>
+      <_VsixDir>$([System.IO.Path]::GetDirectoryName ($(VsixPath)))</_VsixDir>
     </PropertyGroup>
   </Target>
   <Target Name="_CopyToBuildConfiguration"
@@ -120,6 +121,10 @@
         SourceFiles="$(OutputPath)$(AssemblyName).vsix"
         DestinationFiles="$(VsixPath)"
     />
+    <Copy
+        SourceFiles="$(OutputPath)Xamarin.Android.Sdk.json"
+        DestinationFolder="$(_VsixDir)"
+    />
   </Target>
   <!--
     This *replaces* `Microsoft.VSSDK.BuildTools.15.0.26201\build\Microsoft.VSSDK.BuildTools.targets`