Add obsolete note to old JSON APIs #3361
Description
We should add some notes that folks should use System.Text.Json APIs instead from now on to APIs under https://docs.microsoft.com/en-us/dotnet/api/system.json.
/cc @carlossanlop
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We should add some notes that folks should use System.Text.Json APIs instead from now on to APIs under https://docs.microsoft.com/en-us/dotnet/api/system.json.
/cc @carlossanlop