R1:d6edc3f4cc1d

Support evaluation of complex tokenizer functions

Summary:
Depends on D19088. Ref T13079.

> Any sufficiently complicated C or Fortran program contains an ad hoc, informally-specified, bug-ridden, slow implementation of half of Common Lisp.
> - Greenspun's Tenth Rule

Move us a step closer to this noble goal.

This doesn't implement any `viewer(project())` stuff but it looks like the API doesn't need to change to do that in the future.

Test Plan: Grimmaced in pain.

Maniphest Tasks: T13079

Differential…