Drop jsonexample (#2089)

Author: domesticmouse

jsonexample/.gitignore

@@ -1,54 +1,10 @@
-# jsonexample
+## `jsonexample` sample retired
 
-A Flutter sample app that deserializes a set of JSON strings using three
-different libraries: `dart:convert`, `json_serializable`, and
-`built_value`.
-
-## Goals for this sample
-
-* Help you decide which of the three most common libraries for
-  deserializing JSON is right for your project.
-* Provide you with example code for deserializing:
-  * Simple and nested objects
-  * Lists of primitive values
-  * Maps containing primitive values
-
-## The important bits
-
-### `json_strings.dart`
-
-The actual JSON to be deserialized.
-
-### `dart_convert`/`json_serializable`/`dart_convert`
-
-These folders contain code used to deserialize the simple and complex
-object models using one of the three libraries. They do the work of
-instantiating models and populating their fields.
-
-### `tab_pages.dart`
-
-Each tab page in the app deserializes one type of data with one library.
-These Widgets show what app code using the above libraries might look like.
-
-## Generating
-
-The lib/build_value and lib/json_serializable use build_runner to generate
-files. If you make a change to these files, you need to re-run the generator
-using `build_runner`:
-
-```
-flutter pub run build_runner build
-```
-
-## Questions/issues
-
-If you have a general question about JSON serialization in Flutter, the
-best places to go are:
-
-* [The FlutterDev Google Group](https://groups.google.com/forum/#!forum/flutter-dev)
-* [The Flutter Gitter channel](https://gitter.im/flutter/flutter)
-* [StackOverflow](https://stackoverflow.com/questions/tagged/flutter)
-
-If you run into an issue with the sample itself, please file an issue
-in the [main Flutter repo](https://github.com/flutter/flutter/issues).
+The `jsonexample` sample has reached the end of it's useful life. It was great code
+when it has written, but the world has changed. Dart 3 introduced Patterns and
+records. There is also various JSON parsing tools like `json_serializable`.
 
+For further information, please see:
+  - The [Dive into Dart's patterns and records](https://codelabs.developers.google.com/codelabs/dart-patterns-records) 
+    codelab for a deep dive into Dart 3's patterns and records with an application to parsing JSON
+  - The Flutter.dev documentation on [JSON and serialization](https://docs.flutter.dev/data-and-backend/serialization/json)