Fix whitespace between numbers and their signs [Rapid Diffs][Diff File]

What does this MR do and why?

• In support of Rapid Diffs - a feature-flagged rewrite (rapid_diffs)
• For part of #498890

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• Removes source whitespace from output HTML.
• Swaps for the correct negative symbol (MINUS_SIGN versus HYPHEN-MINUS).
• Adds spacing between the added and removed numbers.

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