R1:b2b739c709aa

Reduce code duplication in Herald fields

Summary:
Ref T8726. I want to modularize values and reduce how hard-coded / copypasta'd they are.

- Rename `get...StandardCondition()` to `get...StandardType()`, since we can drive both conditions and values from it.
- Rename `STANDARD_LIST` to `STANDARD_PHID_LIST` for consistency: all "lists" are lists of PHIDs.
- For all standard types which don't require typehaeads, lift their logic into the base class.
- I'll lift typeaheads soon, but need to…