Add Task-returning templates

I couldn't find any templates for Task return types, this makes it hard to use the templates in an async/await environment. It would be very useful if Task-wrapped return types could be added.

Start by locating the existing return-type templates and the template generator entry points in the repository, then compare how synchronous return types are represented. Add equivalent Task-wrapped return types for async/await use and verify that the generated templates are available alongside the existing ones.

Written by the indexing model from the issue text.