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ICU-20659 Fix DTD link in XML data files
ICU-21581 integrate CLDR 40a0 to ICU trunk
ICU-23364 Implement support for the new CLDR dayOfMonths resource in ICU, along with unit tests. This PR also includes a temporary version of the relevant CLDR data (to be overwritten by the next CLDR integration) and an update to the CLDR-to-ICU tool to account for the new resource.