test(formatter): add protected text corpus guards

[MayerTim]

Summary

• Add a Watcom corpus fixture for query clauses mixed with strings, comments, quoted identifiers, and bracketed keyword identifiers.
• Add a Watcom corpus fixture for control-flow words inside comments and string literals alongside a compact CASE expression.
• Preserve current formatter behavior with expected-output and idempotency checks.
• Keep this branch test-only with no extension behavior or formatter default changes.

Validation

• npm run test:corpus
• npm run validate
• npm run package:vsix

Notes

This PR strengthens protected-text regression coverage before tokenizer or formatter refactor work. It does not change formatter implementation or product behavior.