refactor(formatter): centralize word scanning helpers

[MayerTim]

Summary

• Add shared formatter scanner helpers for SQL word-start, word-part, next-word, previous-word, and outside-segment word collection.
• Add parenthesis-depth-aware word collection for structural formatter passes that already track top-level SQL words.
• Replace duplicated local word-scanning loops in Watcom structural formatter passes.
• Preserve the existing scanner state model, protected-text boundaries, formatter behavior, and formatter pass order.

Validation

• npm run validate
• npm run package:vsix
• [x ] npm run test:extension

Notes

This PR is behavior-preserving. It does not change formatter output, formatter pass order, formatter defaults, metadata behavior, diagnostics behavior, extension behavior, packaging behavior, tokenizer architecture, or public documentation.