Add more support for SVG related self-closing tags in Document filter

There are many empty elements in SVG than just `circle`, `g` and `path` tags. For example:

* `use`
* `rect`
* `image`
* `polygon`
* `ellipse`
* etc

Technically in SVG (as XML), any element can be self-closing, even if they aren't defined as empty (e.g. `g`).

Should this not be comprehensive? Or is it exclusively just to make the tests pass?

cf. https://github.com/ampproject/amp-wp/pull/6657#discussion_r737677111

_Originally posted by @westonruter in https://github.com/ampproject/amp-toolbox-php/pull/210#r737734123_