* @summary Return the start of a decade for the given date.
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*
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* @description
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* Return the start of a decade for the given date.
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*
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* @typeParam DateType - The `Date` type, the function operates on. Gets inferred from passed arguments. Allows to use extensions like [`UTCDate`](https://github.com/date-fns/utc).
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*
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* @param date - The original date
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*
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* @returns The start of a decade
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*
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* @example
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* // The start of a decade for 21 October 2015 00:00:00: