fix($shared-utils): Slugify em/en dash in urls

[wdporter]

Summary

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Build-related changes
• [*] Other, please describe:

enhancement, added to the range of characters handled by markdown.slugify

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• Yes
• [*] No

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• When resolving a specific issue, it's referenced in the PR's title (e.g. fix #xxx[,#xxx], where "xxx" is the issue number)

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Other information:

[wdporter]

my headings use a lot of en dash or em dash (unicode 2013, 2014), and they really should just be ignored in the slugify functions, instead i'm getting "%E2%80%93" in my slugs for them (and 94)

[kefranabg]

Thanks @W-David-Porter, one more review and we'll get this merged 👍