feat: fill out answer models

[kamranayub]

TODO

• Text,
• Choice,
• Choices,
• Email,
• Url,
• FileUrl,
• Boolean,
• Number,
• Date,
• Payment

Figure Out

This will be interesting to do on stream:

• Use struct instead of class due to Indicate that a non-nullable Field must be initialized where the type is constructed dotnet/csharplang#2328?
• How to handle discriminator type (enum, string, etc.)
• How to handle deserializing to correct answer type
• Write tests

Resources

• https://docs.microsoft.com/en-us/dotnet/standard/serialization/system-text-json-converters-how-to?pivots=dotnet-6-0#support-polymorphic-deserialization
• https://stackoverflow.com/questions/58074304/is-polymorphic-deserialization-possible-in-system-text-json/59744873#59744873
• https://docs.microsoft.com/en-us/dotnet/api/system.text.json.serialization.jsonstringenumconverter.-ctor?view=net-6.0#System_Text_Json_Serialization_JsonStringEnumConverter__ctor_System_Text_Json_JsonNamingPolicy_System_Boolean_
• https://www.nuget.org/packages/Macross.Json.Extensions/2.2.0-beta2
• System.Text.Json: JsonStringEnumConverter ignores its JsonNamingPolicy during deserialization. dotnet/runtime#31619
• Make JsonStringEnumConverter support nullable enums dotnet/runtime#30947
• https://github.com/Typeform/js-api-client/blob/master/src/typeform-types.ts