Update LanguageTrTest::testDottedAndDotlessI for PHP 7.3
PHP 7.3+ uses Unicode CaseFolding.txt for case mappings. For Turkic
languages(tr,az) the dotted i is given as a special case and we need
to implement it specifically for tr and az.
Updated the documentation and refactored the lcfirst and ucfirst methods
to use arrays containing the above mentioned special cases.