Var::NativeFunction as std::function

by doing this i have done unit tests locally, and wanted to add to the pull requests, but there is no guideline where those tests should live. i’ve noticed some cpp have defined tests inline with the classes but that’s sparse unit testing and i don’t like it. would be cool to have a unit test folder per module where we can check all of them at once and add them more easily. this way you ensure that any contribution or pull requests will add sanity checks to spot problems that “knowledge” and “experience” cannot spot by themselves alone…

TDD is one thing that needs some love and reorganization in juce imho…