R1:a9caab49f7b5

Begin modularizing Herald field values

Summary:
Ref T8726. I'm primarily trying to modularize tokenizer values so we don't have to update JS to add a new one.

This is ultimately the blocker for "select" custom fields working in Herald.

This inches us toward that. I'm //not// modularizing conditions or control types in this round, but hope to end up with hard-coded conditions (which are highly general and very rarely change), hard-coded control types (which are also highly general and very rarely change)…