JsonHelper.IsValid is not matching some JSON structures

[a-khanna]

This PR corrects JsonHelper.IsValid and JsonHelper.Format to support some valid Json inputs like "foo", 123, and null

Pull request type

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• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
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What is the current behavior?

Issue Number: #243

What is the new behavior?

JsonHelper.IsValid now returns true for Json inputs like "foo", 123, and null

Other information

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• Followed the code style guideline as described in CONTRIBUTING.md
• Verified that the change work in Release build configuration
• Checked all unit tests pass

[veler]

Hello, thank you for proposing this fix, and sorry for not taking action on this issue before!
The PR looks all good to me. I will merge it. :)
Have a great day !