## About the PR
Fixes some issues with working with AsyncApiAny, figuring out the correct types etc.
Added new GetValue type methods for extracting expected values.
These use `system.text.json` to deserialize to `T` from the `JsonNode` type.

Added a static FromExtension method, to remove redundant type casting.
So instead of 
```csharp
if (TryGetValue(key, out IAsyncApiExtension extension))
{
  var myType = (extension as AsyncApiAny).GetValue<MyType>();
}
```
You do
```csharp
if (TryGetValue(key, out IAsyncApiExtension extension))
{
  var myType = AsyncApiAny.FromExtensionOrDefault<MyType>(extension);
}
```

Added new constructor allowing for much simpler `AsyncApiAny` initialization, utlizing `system.json.text` to figure out the JsonNode type.

### Changelog
- Added: `GetValue<T>()`
- Added: `GetValueOrDefault<T>()`
- Added: `TryGetValue<T>()`
- Added: static `FromExtensionOrDefault<T>(IAsyncApiExtension extension)`
- Added: new constructor to allow for easier object creation.
- Obsoleted: `AsyncApiArray`
- Obsoleted: `AsyncApiObject`

Co-authored-by: Alex Wichmann <VisualBean@users.noreply.github.com>