[.NET 6] remove usage of System.Json

[jonathanpeppers]

The System.Json package will not work in .NET 6. (Note this isn't the new System.Text.Json.) System.Json is a deprecated package that they don't have a way to ship an update.

It appears we use this as a dependency of Xamarin.GooglePlayServices.SafetyNet:

GooglePlayServicesComponents/source/GooglePlayServicesProject.cshtml

Lines 254 to 257 in 6c65b4e

	@if (@Model.NuGetPackageId == "Xamarin.GooglePlayServices.SafetyNet")
	{
	<PackageReference Include="System.Json" Version="4.5.0" />
	}

Can we remove System.Json in favor of something else? Thanks!

[akoeplinger]

It'd be enough to remove the package for net6.0 and up if you don't want to change how it works on existing Xamarin.

[jpobst]

It looks like our usage of if it is pretty minimal:

https://github.com/xamarin/GooglePlayServicesComponents/blob/main/source/com.google.android.gms/play-services-safetynet/Additions/Additions.cs#L32-L34

[moljac]

Tried to remove it, but decided to finish updates first and make it in another PR.

System.Json.JsonObject.Parse() must be replaced with System.Text.Json.JsonDocument.Parse()

[akoeplinger]

This was done with #480 right? Or is there still something missing?

[moljac]

yes. It was done with #480, but issue and PR were not linked, so this issue was not closed.

Closing it right now.