Normalize array properties

[VasekPurchart]

So that configuration options in XML can be written on multiple lines as in FullyQualifiedClassNameAfterKeywordSniff, FullyQualifiedExceptionsSniff or ReferenceUsedNamesOnlySniff.

With this normalization for example namespaces can be configured in a much more readable and diff-friendly way:

    <rule ref="SlevomatCodingStandard.Files.TypeNameMatchesFileName">
        <properties>
            <property name="rootNamespaces" type="array" value="
                SlevomatCodingStandard => SlevomatCodingStandard,
                tests => SlevomatCodingStandard
            "/>
        </properties>
    </rule>

[Vrtak-CZ]

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