test(formatter): add exception handler corpus guards

[MayerTim]

Summary

• Add a Watcom corpus fixture for EXCEPTION WHEN OTHERS THEN BEGIN ... END indentation.
• Add a Watcom corpus fixture for ON EXCEPTION RESUME, exception declarations, SQLSTATE, and protected exception-handler words inside comments and string literals.
• 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 fills a small corpus coverage gap identified by the private coverage inventory. It does not change formatter implementation, formatter defaults, extension behavior, product behavior, or public documentation.