Add function-lookup() to default function registry

[aj-stein-gsa]

User Story

Per shared interest from @wandmagic and the rest of the FedRAMP Automation Team, I would like us to include function-lookup() to the default function registry for Metapath.

NOTE: This function is not listed as a TODO in the registry as of the current state of DefaultFunctionLibrary.java in develop, which seems odd. I found some Saxonica documentation which explained the legacy function-available() is not what we need for XPath 3.1, but not sure how it evaded Dave's earlier dump of the spec to text, but here we are.

Goals

• Allow general runtime safety to check for missing functions
• Allow developers to code "pre-check" constraints with external constraint files to introspect the runtime and gracefully fail when users accidentally check instances against models with older versions of the tool moving forward to know that function is not yet implemented.

(Yes, ironically this function was perhaps the very first one we should have implemented so long ago, but oh well. 🤣)

Dependencies

N/A

Acceptance Criteria

• All website and readme documentation affected by the changes in this issue have been updated.
• A Pull Request (PR) is submitted that fully addresses the goals of this User Story. This issue is referenced in the PR.
• The CI-CD build process runs without any reported errors on the PR. This can be confirmed by reviewing that all checks have passed in the PR.

Revisions

No response

[wandmagic]

NICE!

[aj-stein-gsa]

NICE!

I never thought I would get this excitement about an issue in an open-source project. I guess we have infected you, @wandmagic.