Pay attention to STU flags on SearchParameter targets

[lmckenzi]

https://jira.hl7.org/browse/FHIR-25744 says that the structuredefinition-standards-status extension should be allowed on SearchParameter.target elements, allowing them to be flagged as STU or draft when the overall shared SearchParameter is normative. The context of the extension allows this, however Kindling needs to be updated to store and propagate the standard level when stored in spreadsheets and to render the appropriate standard status information when displaying the SearchParameter in associated resources. Once this is done, we can update the targets in normative search parameters where some of the targets are non-normative.