Add missing regex description

[adegeo]

Summary

• Fix the linked issue, which added the \p{Mn} to the class description. I also reordered it to match the table.
• Migrated C# code.
• Migrated VB code.
• Fixed older article migration problems (double spaces at the end of the line, bad indentation, etc)
• Upgraded acro score from 71 to 78. (tough to go further without a complete rewrite as acro is really sensitive to the way regex is talked about)

Fixes #43928

Important

Snippets don't actually fail. Removing the old snippets but then discovering that one snippet is used by a different article, causes the build to fail because it think's we're touching the bad area, when we're not. Normally you would remove all snippets from the folder but I don't want to touch the other article unless we move all the snippets in that article, which is out of scope.

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Internal previews

📄 File	🔗 Preview link
docs/standard/base-types/character-classes-in-regular-expressions.md	Character classes in regular expressions

[BillWagner]

This is awesome @adegeo

Let's