This replaces the `Then(string activityName)` method with `ThenNamed(string activityName)`.
A new method is added to allow connecting to activities by type name: `ThenTypeNamed(string activityTypeName)`.
The reason for this change and addition is to allow workflow builders to connect to activity types that do not have a corresponding type.
For example, the Telnyx project has an activity type provider that *dynamically* provides activity types based on Telnyx webhook callback types.
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