Don't force term names to lowercase in definition lists

[kfranqueiro]

This fixes a couple of issues in the build system that I noticed while reviewing #3038:

• A few term names (e.g. ASCII art) have uppercase letters, which the build was forcing to lowercase (this was apparently also true of the XSLT build, judging by e.g. https://www.w3.org/WAI/WCAG21/Understanding/non-text-content#dfn-ascii-art)
• Any linked terms containing newlines would not be recognized (none of these currently exist, but Editorial suggestions for consistent links to definitions and capitalization #3038 added one, which I worked around in that PR so it's not blocked on this)

I also noticed that the term "cognitive function test" includes a capital C, but doesn't seem to warrant one (typically the only term capitalization is for acronyms or proper nouns). (EDIT: removed this part, as Kevin pointed out it is addressed in another issue + open PR)

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[w3cbot]

kfranqueiro marked as non substantive for IPR from ash-nazg.

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[iadawn]

Remove change in case for 'cognitive function test'. This is raised and addressed via #3942

Otherwise, fine.

[kfranqueiro]

Remove change in case for 'cognitive function test'. This is raised and addressed via #3942

Done, thanks for spotting that!