Credit for #6904 (#6925)

* feat: add full support for ValueSet filters in in-memory terminology validation

This adds support for all FHIR-defined ValueSet filter operators
(e.g. is-a, descendent-of, is-not-a, in, regex, exists, etc.) to the in-memory
terminology validator (InMemoryTerminologyServerValidationSupport).

Supports:
- Structural filters: is-a, descendent-of, is-not-a, generalizes, child-of, descendent-leaf
- Equality/regex/inclusion: equal (=), regex, in, not-in
- Existence: exists

Adds internal indexing for concept code/display fields to enable efficient traversal
and matching. Follows case-sensitivity rules defined by CodeSystem.

Also includes a full unit test suite for all filters, covering both code and display
properties where relevant.

Fixes issues where descendant-based filters were not honored during expansion in
tests relying on in-memory terminology (e.g. no JPA preload).

Fixes #4447, #6255

* fix(validation): error on filtered ValueSet includes against ignored CodeSystem

When a ValueSet include specifies filters (e.g. “is-a”) but the referenced CodeSystem is
configured as NOT_PRESENT/ignored, in-memory expansion cannot apply structural filters.
Add a guard to throw an ExpansionCouldNotBeCompletedInternallyException in this scenario
rather than silently returning an empty result.

* test(validation): expect in-memory validation to fail for delta-based hierarchy

Previously we asserted success on an in-memory hierarchy check, but the expander
cannot apply ISA filters against a NOT_PRESENT CodeSystem patched only via
`$apply-codesystem-delta-add`. Update the test to assert that
`validateCode(...)` returns a non-OK outcome containing “cannot apply filters”
for the in-memory pass, then continue to validate via the deferred/pre-expanded path.

* Add changelog for #6904

---------

Co-authored-by: Ibrahim Tallouzi <[email protected]>

Author: jamesagnew

hapi-fhir-docs/src/main/resources/ca/uhn/hapi/fhir/changelog/8_4_0/6904-add-filter-to-inmem-vs-expandeer.yaml

@@ -0,0 +1,6 @@
+---
+type: add
+issue: 6904
+title: "The in-memory ValueSet expander, used for validation outside of JPA, and for validation
+  of ad-hoc and not pre-expanded ValueSets, now supports filtered inclusion/exclusion with a
+  similar scope to the JPA pre-expander. Thanks to Ibrahim Tallouzi for the contribution!"