To avoid problems with `export` statements in the QuickJS Javascript Engine, we can work-around that by *explicitly* exposing `pdfjsScripting` globally instead.
This brings the new `pdf.scripting.js` bundling more in-line with the pre-existing handling for the `pdf.js`/`pdf.worker.js` files:
- Add a new `src/pdf.scripting.js` file as the entry-point for the build scripts.
- Add the version/build numbers at the top of the *built* `pdf.scripting.js` files, since all other built files include that information given that it's often helpful to be able to easily determine the *exact* version.
- Tweak the `createScriptingBundle` in the gulp-file, since it looks like a little bit too much copy-and-paste in the variable names.
