Adding textDocument\foldingRange support for the language server

[tmcrain]

Is your feature request related to a problem? Please describe.
Being able to collapse long docstrings/adjacent single line comments/adjacent open statements into single lines can greatly improve readability (prime example: Quantum Katas, Basic Gates task).

Describe the solution you'd like
Support for the textDocument\foldingRange language server protocol message.

Describe alternatives you've considered
N/A

Additional context
Currently working on this for the OneWeek hackathon!

[tmcrain]

On hold until the Visual Studio SDK is updated to >= 16.1.3121, which depends on this issue being fixed.

[bettinaheim]

@tmcrain Is there a branch with the WIP? Also, let me know if you feel like picking up something else. :)

[bettinaheim]

Looks like the blocking issue above has been fixed.
@tmcrain, are you still interested in picking this up? :)