[tests] Let Xamarin.Android-Tests.sln load in VSMac without errors (d…

…otnet#4489)

Context: https://docs.microsoft.com/en-us/visualstudio/extensibility/internals/adding-items-to-the-add-new-item-dialog-boxes?view=vs-2019

The VSMac was complaining when loading
`tests/Xamarin.Forms-Performance-Integration`:

	Error while trying to load the project 'tests/Xamarin.Forms-Performance-Integration/Xamarin.Forms.Performance.Integration.csproj':
	Project Xamarin.Forms.Performance.Integration is being loaded as a Shared Assets project but has a different file extension.
	Please check the project type GUID in the solution file is correct.

The problem was because `Xamarin.Forms.Performance.Integration.csproj`
was within the `.sln` as a "Shared Project" -- see this
[list of project type GUIDs][0] -- and the fix is to instead specify
the C# Project Type.

[0]: https://stackoverflow.com/questions/10802198/visual-studio-project-type-guids

Xamarin.Android-Tests.sln

@@ -52,7 +52,7 @@ Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Xamarin.Android.BindingReso
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Xamarin.Android.BindingResolveImports-Tests", "tests\ResolveImports\Xamarin.Android.BindingResolveImports-Tests\Xamarin.Android.BindingResolveImports-Tests.csproj", "{B297008B-C313-455E-B230-E119589D2D79}"
 EndProject
-Project("{D954291E-2A0B-460D-934E-DC6B0785DB48}") = "Xamarin.Forms.Performance.Integration", "tests\Xamarin.Forms-Performance-Integration\Xamarin.Forms.Performance.Integration.csproj", "{195BE9C2-1F91-40DC-BD6D-DE860BF083FB}"
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Xamarin.Forms.Performance.Integration", "tests\Xamarin.Forms-Performance-Integration\Xamarin.Forms.Performance.Integration.csproj", "{195BE9C2-1F91-40DC-BD6D-DE860BF083FB}"
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Xamarin.Forms.Performance.Integration.Droid", "tests\Xamarin.Forms-Performance-Integration\Droid\Xamarin.Forms.Performance.Integration.Droid.csproj", "{576312CC-83FF-48B1-A473-488CDC7121AD}"
 EndProject