Synchronize improvements to cppreference once it becomes editable again

[frederick-vs-ja]

It's probable that some improvements will be made when porting contents from cppreference. Currently (2025-12-12), cppreference is not editable. We should record these improvements somewhere and synchronize them to cppreference whenever possible.

[frederick-vs-ja]

• https://en.cppreference.com/w/cpp/preprocessor.html
  • Rephrase "non-standard extension" to "extension" because it's unlikely to categorize some extension as standard. update preprocessor documentation #52

[Sudrut]

After we have completed the migration of the English content and begin migrating the translated pages, we will also need to know where we made improvements.

[frederick-vs-ja]

After we have completed the migration of the English content and begin migrating the translated pages, we will also need to know where we made improvements.

This should be able to be done during review.