Consider fixed value for single-option code filters

Currently, all code filters get placed in narrative tables. however, there are some situations where there are constraints on elements like status (e.g., Encounter.status = completed on the BMI screening measure (CMS69: [PCSBMIScreenAndFollowUpFHIR](https://ecqi.healthit.gov/sites/default/files/ecqm/measures/CMS69v9.html))). Should these be represented as fixed code values instead? Probably would happen very rarely because the code filter would need to apply to all instances of the profile used by all measures. This may need to be moved forward here or to an upstream measure development process.