fix(benchmark): enable all polyglot exercise tests - #5905

Summary

• enable JavaScript tests declared with xtest, xit, test.skip, or it.skip
• enable Java tests declared with either @Disabled or @Disabled(...)
• centralize the transformations in a small reusable helper
• add regression coverage for activation, idempotence, unchanged active tests, and file updates

Impact check

I scanned the current Aider-AI/polyglot-benchmark repository for skip forms not handled by the existing runner. The scan confirmed the four files reported in #5898:

• grep.spec.js: 23 missed tests
• palindrome-products.spec.js: 1 missed test
• robot-name.spec.js: 1 missed test
• ForthEvaluatorTest.java: 1 missed test

Running the new normalization on those files removed all 26 unsupported skip markers. Ordinary active tests, comments, and string examples remain unchanged.

Tests

• python -m pytest benchmark/test_enable_tests.py -q (8 passed)
• Black, isort, flake8, codespell, and git diff --check

Closes #5898