Make Style/RedundantPercentQ handle multiline source safely

[boardfish]

The regex used in Style/RedundantPercentQ is not resilient to multiline input, meaning that its autocorrect would unsafely operate on strings defined across multiple lines with %Q where these used quotes. This PR changes the anchors on the regex used by the cop so that its autocorrect determines the correct delimiter safely.

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• Added tests.
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