Populate "path" property in FHIRPathNode implementations representing system values

[jarrettranderson]

Is your feature request related to a problem? Please describe.
We have a requirement to remove the "id" property from certain elements of a resource. Consistent with other planned operations, we would find the targets using a FHIRPath expression and then remove them using FHIRPathUtil.delete(). FHIRPathUtil.delete() requires the path to the target, but the path() method returns null for FHIRPathStringValue objects returned from the FHIRPath evaluation.

Describe the solution you'd like
The path() method in FHIRPathStringValue objects and probably other FHIRPathSystemValue implementations should return the path to the node like it does for other implementations of FHIRPathNode.

Describe alternatives you've considered
For this particular scenario, we could use FHIRPath to find all the Element type objects in the tree and check each of them to see if the "id" value is populated. We would then update the parent object in a different manner.

Acceptance Criteria
1.
GIVEN [a FHIRPath expression that targets "id" or another system value field, such as "descendants().select(id)"]
AND [EvaluationContext evaluationContext = new EvaluationContext(some-resource)]
WHEN [FHIRPathEvaluator.evaluator().evaluate(evaluationContext, fhir-path-expression]
THEN [for each object returned, path() is non-null]

Additional context
Add any other context or screenshots about the feature request here.

[lmsurpre]

Info for executing the fhir-path cli jar can be found at https://github.com/IBM/FHIR/tree/main/fhir-path

[lmsurpre]

One of the primary motivations for this issue is to be able to work with the 'Element.id' attribute from our FHIRPathPatch engine. Previously we had some "interesting" behavior for this attribute where it would fight with the 'value' attribute on primitives.

To verify that part of the fix I recommend the followings:

1. post a resource to the server that includes elements with ids
2. issue a FHIRPathPatch the removes one of the ids from a primitive datatype and the value from a different one
3. read the resource and confirm it looks right

[lmsurpre]

Per the above I posted the following resource:

{
  "resourceType": "Patient",
  "id": "{{patient}}",
  "language": "en",
	"text": {
		"status": "empty",
		"div": "<div xmlns=\"http://www.w3.org/1999/xhtml\">Lee (1234)</div>"
	},
  "identifier": [{
    "use": "usual",
		"_use": {
			"id": "my-primitive-extension",
			"extension": [{
				"url": "http://example.com/primitive-extension",
				"valueString": "test1"
			}]
		},
		"system": "https://example.com",
		"value": "1234"
  }],
	"name": [{
		"given": ["Lee"],
		"_given": [{
			"id": "my-repeat-primitive-extension",
			"extension": [{
				"url": "http://example.com/primitive-extension",
				"valueString": "test2"
			}]
		}]
	}],
  "active": true
}

Then I removed the Patient.identifier.use.id element via a patch like this:

{
	"resourceType": "Parameters",
	"parameter": [
		{
			"name": "operation",
			"part": [
				{
					"name": "type",
					"valueCode": "delete" 
				},
				{
					"name": "path",
					"valueString": "Patient.identifier.use.id"
				}
			]
		}
	]
}

@d0roppe feel free to do some related testing

[lmsurpre]

seems to be working