Validators for filter fields

Allow passing in `[["filterA", v.string()], ["filterB", v.number()]]` OR `["filterA", "filterB"]` that validate on write & parse on read, instead of a type param

Start by locating the filter-field handling entry point in the TypeScript component and trace how values are written and parsed on read. Done means supporting both validator pairs such as [["filterA", v.string()]] and plain field-name arrays such as ["filterA", "filterB"], with validation on write and parsing on read.

Written by the indexing model from the issue text.