add launch.json to debug F# in vscode with sourcemaps support for fable/Feliz side

[jkone27]

seems not trivial to debug client side code in vscode in the current setup,

would be great to be able to debug code on the client side in .fs too

[jwthomson]

It is fair to say that it is not trivial to debug client side code in VS Code, I spent a while trying to figure out how to achieve this in December but couldn't find a satisfying solution.

For debugging I use the broswer tools since that's ultimately where it is being run but maybe someone who is more familiar with VS Code has a better solution.

Sorry that this is not a satisfying response!