Grafast: hoisting of subroutines

[benjie]

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.