Add ability to disable one of Babel or TypeScript transpilation, but not the other

I'm working on a project that uses both Babel and TypeScript. It has a dangerfile written in TypeScript that imports a JavaScript file. That JS file in turn imports a JS file from a package in `node_modules`. The issue is that the JS file uses the `new` keyword to instantiate an ES6 class defined in the JS file from the package. Danger uses Babel to transpile the file to ES5. The transpiled code doesn't use `new` to instantiate the ES6 class (which isn't transpiled because it's in `node_modules`), leading to a `Class constructor ClassName cannot be invoked without 'new'` error.

I know that there's a way to disable all transpilation. However, I want to keep transpiling TypeScript so that I can write the dangerfile in TypeScript. It would be useful to just be able to disable Babel transpilation while continuing to transpile TypeScript (or maybe vice versa for a different use case).

No file or test is named. Start by locating the transpilation configuration and the code paths that invoke Babel and TypeScript; done means users can independently disable either transformer while the other remains active, including the reported JavaScript/TypeScript import case.

Written by the indexing model from the issue text.