Encapsulate page layout for extensions

[Bellangelo]

Partially addresses: #1823

This commit re-enables the page building of the extension which was disabled in #3212.

I have no idea why it was disabled but in production it produces a 404 link. You can check it here https://spec.openapis.org/registry/extension/index.html by clicking on the x-twitter link.

A rendered result can be seen here: https://bellangelo.github.io/OpenAPI-Specification/registry/extension/x-twitter.html

[handrews]

@OAI/tsc based on #3212 there was a conscious decision to hide this registry- anyone recall why this was done and whether we should bring it back or just delete it?

[ralfhandl]

As far as I can recall the discussion, the extension registry is practically not used and its only entry may already be obsolete. Better keep it hidden, and also hide the menu entry for it in the left side bar:

[Bellangelo]

As far as I can recall the discussion, the extension registry is practically not used and its only entry may already be obsolete. Better keep it hidden, and also hide the menu entry for it in the left side bar:

Thanks for your input @ralfhandl, should we delete it then? I don't see why we should keep it if it hidden. If anyone wants to "re-enable" it later on, he can just look at the git history.

[lornajane]

Thanks for finding and rescuing this