Replaced Newtonsoft.Json with System.Text.Json in projects. Plus minor misc fixes.

[pmaytak]

Replaced Newtonsoft.Json with System.Text.Json in projects (including samples). Plus minor spelling, warning fixes.

Note: Newtonsoft.Json by default does case-insensitive deserializaton, while System.Text.Json is case-sensitive by default to improve performance. In order to make it case-insensitive, we have to pass it options object to the deserializer.

Related resources:
Try the new System.Text.Json APIs
How to serialize and deserialize (marshal and unmarshal) JSON in .NET
How to migrate from Newtonsoft.Json to System.Text.Json

[jmprieur]

LGTM.
I'm just wondering why we need to change the samples.

[jmprieur]

Thanks for clarifying Peter.
Next time there is an impact on a sample:

• if this is due to the change to the product code. Fine.
• however if this is a different work item (like here), please:
  • create a new GitHub issue to prioritize the work
  • propose a second PR