Improve TokenUtils performance through caching

For #9717.

For testing, you can take https://gist.github.com/MarcelGerber/5c11f1031af292044708, placing your cursor in the script tags and pressing `Ctrl-Space`.
I actually found out that Lodash has a binary search function (`_.sortedIndex` - is there anything that's not in Lodash?!) and well, I used it :)