Support "Run function" inline hints

[santiweight]

In major languages' IDEs, there will often be support for inline actions that allow running a main function. For example, Scala has the following action:

If we notice that a function is IO (), then we could surely run it I imagine? I'm not sure who wrote the eval plugin, but this would be right up their alley!

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A potential extension to this was discussed on discourse: https://discourse.haskell.org/t/hf-coordination-for-test-framework-ide-integration/5221/2?u=santiweight

One can imagine supporting some of the following use cases:

• Support running TestTree's and the like from tasty or hspec
• One could imagine supporting a code action that generates some random data for a function. For example, if we have a function foo :: Int -> Bool -> Int, we could provide a few random arguments and show the user what happens...