Provide custom data type to hold data source entries

[Evangelink]

As alternative to IEnumerable<object[]> and IEnumerable<(Value)Tuple<...>> we could offer a new type, that people could use for their data source.

For inspiration, xUnit has TheoryData which provides type-safe dynamic data.
See e.g. https://andrewlock.net/creating-strongly-typed-xunit-theory-test-data-with-theorydata/.
Especially the last code-snippet shows how how concise it can be used.

Originally posted by @jnyrup in #1335 (comment)

AB#2332769