Have a consistent opening paragraph for HTML elements

[wbamberg]

This issue is to make the opening paragraph of our HTML elements consistently begin with a sentence of the form:

"The $element_name HTML element ..."

...where $element_name is the element name including angle brackets, in <strong> tags, and "HTML" is a link to https://developer.mozilla.org/en-US/docs/Web/HTML. For example:

The <div> HTML element

This reflects the consensus in https://github.com/mdn/content/discussions/5131.