Don't strip invalid characters from ImplementationGuide name (#1271)

[cpruijsen]

Description:

SUSHI was quietly removing non-alphanumeric characters from ImplementationGuide.name (except _) and not capitalizing the first letter, so the result could still violate FHIR name.matches('[A-Z]([A-Za-z0-9_]){0,254}').

initIG now assigns config.name as authored. If the name is present and does not match that constraint, SUSHI logs a warning that quotes the constraint and points at the "name" property in sushi-config.yaml. It does not auto-capitalize and does not keep stripping.

This matches how Profile / ValueSet / CodeSystem names are already handled (HasName.setName): leave the value, warn, let the author fix it.

What I chose and the alternative: leave the name as authored and warn. The alternative is to keep stripping (and maybe capitalize the first letter) and also warn. I chose leave-and-warn because that is what #1271 asks for, and because silent cleanup was the confusing part, including cases like Minimal IG that used to become a FHIR-valid MinimalIG with no log. Happy to switch if maintainers would rather share nameRegex from mixins.ts, keep a sanitized export plus a warn, or treat this as an error instead of a warning.

Testing Instructions:

• npm test -- test/ig/IGExporter.test.ts
• In a project whose sushi-config.yaml has name: Minimal IG, confirm the generated ImplementationGuide-*.json keeps name: "Minimal IG" and the build log warns with [A-Z]([A-Za-z0-9_]){0,254}.
• With name: MinimalIG, confirm the name is unchanged and that constraint warning is not emitted.

Note: authors who previously relied on SUSHI stripping spaces or hyphens will now export the invalid name and see a warning (and IG Publisher may reject it) until they fix sushi-config.yaml. Use title for the human label; name is the machine identifier.

Related Issue:

Fixes #1271

[cmoesel]

Thanks for the contribution, @cpruijsen. This looks great. The warning message is helpful too. Approved!

Thanks again!