Feature: Migrate from Newtonsoft.Json to System.Text.Json

### What's the Problem?

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### Solution/Idea

After migrating to WinAppSDK, we now have the option to migrate from Newtonsoft.Json to System.Text.Json. Doing this will remove an extra dependency and improve performance.

### Alternatives

na

### Priorities

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### Files Version

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### Windows Version

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### Comments

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