R1:7711ea9855ed

Move handle fetching into tokenizer Datasources

Summary:
Ref T7689. This serves two goals:

- I want to remove Controller->loadViewerHandles(). A nontrivial number of these callsites are loading handles to pass to tokenizers. Since tokenizers need to take strings eventually anyway, we can do less work by letting them take PHIDs now.
- A few changes out, I want tokenizers to accept parameterized tokens (like `viewer()`, `members(differential)`, etc.), so the `setValues()` signature needs to change…