Do not allow not passing a body to an HTML element function

Description

HTML element functions (functions of the html module that return an html.elem, part of the typed HTML API) that accept a body should not allow not passing it.

Use Case

HTML element functions can be called without specifying a body. For example, the calls html.div() and html.html() are valid, and equivalent to html.div[] and html.html[] respectively.

This can be confusing as no error is emitted in the following case, where .with was unintentionally omitted:

#show: html.html(lang: "en")

I believe it is better to be explicit and pass an empty body if wanted rather than not getting an error when no body is provided.

Note that some standard library functions that accept a body already require that body to be provided (e.g., place, align, link), while others don't, like block, box, or rect whose bodies are not only optional but also settable.

Start by tracing the typed HTML API's HTML element functions and compare their body handling with standard-library functions such as place, align, link, block, box, and rect. Determine which HTML functions should require an explicit body while preserving intentionally optional or settable bodies. Done means calls such as html.div() and html.html() produce an error, while explicit empty bodies remain valid.