[C#] Update InputHelper to be static

[ryan-linehan]

Is your feature request related to a problem? Please describe.
It would be nice if InputHelper did not have a requirement to inherit node. I can't say for certain since I am eyeballing it but don't see a reason for it to inherit node in the c# script

Describe the solution you'd like
Instead of InputHelper inheriting node and all that comes with it the c# input helper class could just not use it. I am unsure if this could be a breaking change or not since the c# class isn't instanced just the static variables and methods are used

Describe alternatives you've considered
N/A