Refactor ActivityDefinitionProcessor to allow for custom activities

[barhodes]

• Fixed numerous issues with FHIRPath evaluation during $apply
• Added support for all possible Request types in ActivityDefinition/$apply
• Added support for Custom Activities in ActivityDefinition/$apply
• Added support for OperationOutcomes for non-fatal exceptions in ActivityDefinition/$apply
• Refactored version specific processors for ActivityDefiintion, PlanDefinition, Questionnaire and QuestionnaireResponse into a single version agnostic processor
• Added support for generating items from profile snapshot elements
• Added support for StructureDefinition/$questionnaire operation

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[codecov[bot]]

Codecov Report

Attention: 562 lines in your changes are missing coverage. Please review.

Comparison is base (bcc436b) 45.14% compared to head (93e0fc9) 52.60%.

Files	Patch %	Lines
...qf/fhir/cr/plandefinition/apply/ProcessAction.java	72.00%	39 Missing and 10 partials :warning:
...f/fhir/cr/plandefinition/apply/ProcessRequest.java	87.50%	14 Missing and 11 partials :warning:
...itydefinition/apply/resolvers/r5/TaskResolver.java	38.88%	14 Missing and 8 partials :warning:
...ion/apply/resolvers/r5/ServiceRequestResolver.java	45.45%	11 Missing and 7 partials :warning:
...cqf/fhir/cr/plandefinition/apply/ApplyRequest.java	89.34%	0 Missing and 18 partials :warning:
.../fhir/cr/questionnaire/generate/ItemGenerator.java	87.58%	9 Missing and 9 partials :warning:
...definition/apply/resolvers/dstu3/TaskResolver.java	53.33%	11 Missing and 3 partials :warning:
...onnaireresponse/extract/ProcessDefinitionItem.java	84.94%	7 Missing and 7 partials :warning:
...estionnaire/populate/ProcessItemWithExtension.java	72.91%	11 Missing and 2 partials :warning:
...fhir/cr/activitydefinition/apply/ApplyRequest.java	80.64%	11 Missing and 1 partial :warning:
... and 68 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #381 +/- ## ============================================ + Coverage 45.14% 52.60% +7.46% - Complexity 1715 2062 +347 ============================================ Files 224 275 +51 Lines 11866 11624 -242 Branches 1661 1582 -79 ============================================ + Hits 5357 6115 +758 + Misses 5875 4907 -968 + Partials 634 602 -32 ```

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