add codelens for running main func

[vuon9]

I've added a codelens for main func #159, here is how it looks like:

Additionally, I thought about another configuration flag to control keeping the output or clear the output, might be go.runMain.cleanPreviousOutput. Hope to hear the feedback.

Updates #159

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Message from Polina Sokolova:

Patch Set 2:

(9 comments)

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