[Feature Request] Switch to System.Text.Json from Newtonsoft.Json

Problem Statement

#9102 asks if AdaptiveCards will switch to System.Text.Json from Netwonsoft.Json opening this feature request to campture that ask.

Migration from Newtonsoft.Json to System.Text.Json details can be found here: Migrate from Newtonsoft.Json to System.Text.Json.

Proposed solution

1. Providing documentation on how the migration from Newtonsoft.Json will happen. Details for proposed solution should be added to this feature request.
2. Implement migration from proposed solution above.
3. Add/update tests.
4. Verify functionality parity with existing version of AdaptiveCards.
5. Update documentation.

Alternatives or Workarounds

No response