Support JSON serialization with System.Text.Json

[hootanht]

Fixes #2495

Add support for JSON serialization with System.Text.Json.

• Add JsonSerializer interface and implement NewtonsoftJsonSerializer and SystemTextJsonSerializer classes in src/Stripe.net/Infrastructure/JsonSerializer.cs.
• Update StripeEntity class in src/Stripe.net/Entities/_base/StripeEntity.cs to use the JsonSerializer interface for ToJson and FromJson methods.
• Replace Newtonsoft.Json attributes with System.Text.Json attributes in src/Stripe.net/Entities/Customers/Customer.cs, src/Stripe.net/Entities/_common/Address.cs, src/Stripe.net/Entities/_common/AddressJapan.cs, src/Stripe.net/Entities/_common/Shipping.cs, src/Stripe.net/Entities/AccountLinks/AccountLink.cs, and src/Stripe.net/Entities/Accounts/Account.cs.
• Add conditional compilation to use appropriate attributes based on the selected JSON serializer in the above files.

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[jar-stripe]

@hootanht Thank you submitting this PR! Supporting System.Text.Json as an alternative to Newtonsoft is on our to-do list for this quarter, and I'd love to work with you on getting this landed. We have a code generator that is responsible for generating some 500-odd files that I definitely don't want to ask you to manually update, and I want to be able to include this in such a way that one SDK will be compatible with users of both Newtonsoft and System.Text.Json. Let me review your changes and see how we can incorporate them into our code generation infrastructure, make sure it won't break existing users, and then I'll plan to push updates right back to this branch/PR. Sound good?

[hootanht]

@hootanht Thank you submitting this PR! Supporting System.Text.Json as an alternative to Newtonsoft is on our to-do list for this quarter, and I'd love to work with you on getting this landed. We have a code generator that is responsible for generating some 500-odd files that I definitely don't want to ask you to manually update, and I want to be able to include this in such a way that one SDK will be compatible with users of both Newtonsoft and System.Text.Json. Let me review your changes and see how we can incorporate them into our code generation infrastructure, make sure it won't break existing users, and then I'll plan to push updates right back to this branch/PR. Sound good?

Awesome 👌

[jar-stripe]

Hi @hootanht ! Just a quick update here; I'm actually considering a more pared down approach here, to reduce the blast zone of a change while still solving the original ticket. I left a comment over on the issue: #2495 (comment), mind giving it a read and chiming in there? Thanks!

[hootanht]

Thanks a lot

[jar-stripe]

Sure thing! And if that doesn't completely work for your use case we can definitely revisit this here. Thanks again!