516 compatibility for simple HTML

[ShiftyRail]

What this does

BYOND 516 no longer let us send uncomplete HTML to render in browser window. Those instead get displayed as raw text.
This PR addresses that by adding a HTML wrapper to all x<< browse(something, "window=x"). This ensures they're properly displayed for a 516 client. The change is not noticeable by 515 clients.

This PR is necessary for #37501 to work, but can be merged as a standalone into the Bleeding-Edge version. 515 clients won't notice anything. 516 clients will have less bugs.

We should, eventually, move away from uncomplete HTML and into browser datums as their code is a bit of a mess (to put it midly). It mixes UI and backend into the same file, it's not reactive, difficult to review, it looks a bit ugly, you need to close the window to see any changes, etc. But that's a lot of effort.

Why it's good

We want to move to 516 at some point.

How it was tested

Minimally if I'm honest. There's like, a hundred or so UIs to test? I just grabbed 2-3 of them and check if they still worked. They do. No problem.

Changelog

🆑

• experiment: 516 clients should no longer have broken HTML windows in some cases (such as using admin verbs).