Add comment line support on testconfig.json when targeting .NET Framework

## Summary JsonConfigurationFileParser support comment and trailing comma when targeting .NET. https://github.com/microsoft/testfx/blob/75f70ecd388358e13d5c8effa6ed21a871adf47c/src/Platform/Microsoft.Testing.Platform/Configurations/JsonConfigurationFileParser.cs#L31-L35 But when using .NET Framework Jsonite library based implementation is used instead. ([JsonConfigurationFileParser.netstandard.cs](https://github.com/microsoft/testfx/blob/75f70ecd388358e13d5c8effa6ed21a871adf47c/src/Platform/Microsoft.Testing.Platform/Configurations/JsonConfigurationFileParser.netstandard.cs#L19-L22)) And comment is not supported because underling Jsonite don't support this feature. **StackTrace** ``` Unhandled Exception: Jsonite.JsonException: Unexpected character '/' while parsing an object. Expecting a STRING or '}' at Jsonite.JsonReflectorDefault.OnDeserializeRaiseParsingError(Int32 offset, Int32 line, Int32 column, String message, Exception inner) in /_/src/Platform/Microsoft.Testing.Platform/ServerMode/JsonRpc/Json/Jsonite/JsonReflector.cs:line 353 at Jsonite.Json.JsonReader.RaiseUnexpected(String message) in /_/src/Platform/Microsoft.Testing.Platform/ServerMode/JsonRpc/Json/Jsonite/JsonReader.cs:line 602 at Jsonite.Json.JsonReader.ParseObject(Object obj, Type expectedType) in /_/src/Platform/Microsoft.Testing.Platform/ServerMode/JsonRpc/Json/Jsonite/JsonReader.cs:line 194 at Jsonite.Json.JsonReader.Parse(Object existingObject, Type expectedType, Boolean expectValue) in /_/src/Platform/Microsoft.Testing.Platform/ServerMode/JsonRpc/Json/Jsonite/JsonReader.cs:line 95 at Jsonite.Json.Deserialize(TextReader reader, JsonSettings settings) in /_/src/Platform/Microsoft.Testing.Platform/ServerMode/JsonRpc/Json/Jsonite/Json.cs:line 84 at Jsonite.Json.Deserialize(String text, JsonSettings settings) in /_/src/Platform/Microsoft.Testing.Platform/ServerMode/JsonRpc/Json/Jsonite/Json.cs:line 69 at Microsoft.Testing.Platform.Configurations.JsonConfigurationFileParser.ParseStream(Stream input) in /_/src/Platform/Microsoft.Testing.Platform/Configurations/JsonConfigurationFileParser.netstandard.cs:line 33 at Microsoft.Testing.Platform.Configurations.JsonConfigurationSource.JsonConfigurationProvider.<LoadAsync>d__14.MoveNext() in /_/src/Platform/Microsoft.Testing.Platform/Configurations/JsonConfigurationProvider.cs:line 85 ``` ## Background and Motivation I want add comment on JSON configuration file. (e.g. add link to available options) But currently it's not works if project contains .NET Framework target. ## Proposed Feature Add support for comment line on Jsonite custom implementation. or preprocess comment lines before parsing JSON config file.