Similar to how the `@babel/core` dependency is managed for the localize
NPM package, the version should be locked. Also the version should
correspond to the version we install for building & testing.

Currently the Babel version allowed by the compiler-cli may not
work given the ESM -> CJS interop. causing errors like:

```
import { types as t } from "@babel/core";
         ^^^^^
SyntaxError: Named export 'types' not found. The requested module '@babel/core' is a CommonJS module, which may not support all module.exports as named exports.
CommonJS modules can always be imported via the default export, for example using:

import pkg from '@babel/core';
const { types: t } = pkg;
```

We can only be confident about the interop if we know the version
installed- is the one we test.