Add TypeInfo::UntypedEnum and TypeInfo::UntypedStruct.

[tritao]

Description

Adds TypeInfo::UntypedEnum and TypeInfo::UntypedStruct, which are used to represent untyped enums/structs pointing to a ParsedDeclId. These will be used for an upcoming PR that does name resolution as a standalone step before type checking.

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
  • If my change requires substantial documentation changes, I have requested support from the DevRel team
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.

[codspeed-hq]

CodSpeed Performance Report

Merging #6633 will improve performances by 21.54%

_{Comparing tritao:typeinfo-untyped (fa8154d) with master (c374a11)}

Summary

⚡ 1 improvements
✅ 21 untouched benchmarks

Benchmarks breakdown

	Benchmark	master	tritao:typeinfo-untyped	Change
⚡	document_symbol	5.2 ms	4.3 ms	+21.54%