Describe the issue
in https://hl7.org/fhir/search_filter.html, _filter syntax should have feature:

A filter can be a logical one (x or x, or x and x, or not x).

and in formal grammar:

filter        = paramExp / logExp / ("not") "(" filter ")"

To Reproduce

1. Choose a filter for example code eq I46.9 in resource Condition
2. Do query using _filter syntax. in test server: https://hapi.fhir.org/baseR4/Condition/?_filter=%28code%20eq%20I46.9%29
3. Make a not logic to filter, for our example: not(code eq I46.9)
4. Do logic query to _filter syntax. in test server: https://hapi.fhir.org/baseR4/Condition/?_filter=not%28code%20eq%20I46.9%29

Expected behavior
2nd step should return Condition with code I46.9
4th stem should return Condition without code I46.9. but I got an error

Environment:

• HAPI FHIR Version: HAPI FHIR 6.7.8-SNAPSHOT/b985091c2c/2023-06-21

Additional context
Add any other context about the problem here.