Add tasks for all the new languages

Task/String-length/Swift/string-length-1.swift

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+let numberOfCharacters = "møøse".characters.count  // 5

Task/String-length/Swift/string-length-10.swift

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+let numberOfBytesUTF16 = "møøse".utf16.count * 2           // 10

Task/String-length/Swift/string-length-11.swift

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+let numberOfBytesUTF16 = count("møøse".utf16) * 2          // 10

Task/String-length/Swift/string-length-12.swift

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+let numberOfBytesUTF16 = countElements("møøse".utf16) * 2  // 10

Task/String-length/Swift/string-length-2.swift

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+let numberOfCharacters = count("møøse")            // 5

Task/String-length/Swift/string-length-3.swift

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+let numberOfCharacters = countElements("møøse")    // 5

Task/String-length/Swift/string-length-4.swift

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+let numberOfCodePoints = "møøse".unicodeScalars.count           // 5

Task/String-length/Swift/string-length-5.swift

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+let numberOfCodePoints = count("møøse".unicodeScalars)          // 5

Task/String-length/Swift/string-length-6.swift

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+let numberOfCodePoints = countElements("møøse".unicodeScalars)  // 5

Task/String-length/Swift/string-length-7.swift

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+let numberOfBytesUTF8 = "møøse".utf8.count           // 7

Task/String-length/Swift/string-length-8.swift

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+let numberOfBytesUTF8 = count("møøse".utf8)          // 7

Task/String-length/Swift/string-length-9.swift

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+let numberOfBytesUTF8 = countElements("møøse".utf8)  // 7