Provide better tests for SVG attributes

[Elchi3]

This PR fixes some SVG attribute tests:

• All xlink_href, xlink_actuate, xlink_show, and xlink_title tests need special handling and so I updated the element test builder. They are used on many SVG elements.
• Several attributes have different names in the SVGOM. I did some replacements in the test builder as they appear many times on various SVG elements as well.

[Elchi3]

oh err "'attrProp' is of type 'unknown'." says Typescript now. I guess I need to tell it a type somehow?

[queengooborg]

Argh, f#&$ing TypeScript... Unfortunately, it doesn't attribute types for Object.entries, which causes lots of issues. If we specify Object.entries(...) as [string, string][], that should fix it?

[Elchi3]

If we specify Object.entries(...) as [string, string][], that should fix it?

I was toying around to figure out how to assign the string type, but I had no idea it is as [string, string][] after Object.entries. Thanks much for the hint!

[Elchi3]

I was about to comment on this PR if I should have updated element.json instead of implementing replacements here.
Basically what I did in #997 (which I just learned about!)

[queengooborg]

Oh! Yes, that would probably be the better option for the non-xlink attributes...I forgot that was a thing, and I'm the one who implemented it! 😆

[Elchi3]

Working on a PR to use that instead!