Grafast: hoisting of subroutines

This example:

https://github.com/scottravio/grafast-memory-spike-repro/blob/bf3b601b50949f81625cc767be5a323d76926f5c/languageplugin.mjs

Creates a subroutine via the `each()` step, but this step isn't dependent on the current user so theoretically it could be hoisted. Current it is not hoisted, which is resulting in the transform being executed NUMBER_OF_USERS * NUMBER_OF_LANGUAGES times, whereas it should only need to happen NUMBER_OF_LANGUAGES times. We should investigate hoisting the subroutine to make these usages more efficient.