fix: Prevent panic in semantic highlighting for unknown token types

[JoshuaBatty]

Description

Previously, the language server would panic if it encountered a SymbolKind that mapped to a SemanticTokenType not present in the SUPPORTED_TYPES array. This was due to an unwrap() call in the type_index function.

This PR addresses the issue by:
Adding SemanticTokenType::new("traitType") to the SUPPORTED_TYPES array, which was the specific missing type causing a crash when opening sway-lib-std/src/iterator.sw.

Modifying type_index to return Option<u32> instead of u32, removing the unwrap().

closes #7188

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 #7189 will not alter performance

_{Comparing josh/lsp_std_lib (bde7580) with master (5a95c65)}

Summary

✅ 24 untouched benchmarks