Implement proposal stated in ADR for setup-dotnet v3 and functionality from feature request #219 (#315)

__tests__/csc.test.ts

@@ -1,5 +1,3 @@
-import fs = require('fs');
-
 describe('csc tests', () => {
   it('Valid regular expression', async () => {
     var cscFile = require('../.github/csc.json');