Generate body of CLDR Hant-Latn transform from 2nd value in 2-value kMandarin entries

[pedberg-icu]

unicodetools already has tooling to generate the main body of the CLDR Han-Latin transform (= Hani-Latn, Hans-Latn) from Unihan kMandarin values; when a kMandarin entry has 2 values, it uses the first. Now per https://unicode-org.atlassian.net/browse/CLDR-18080 we have added a Hant-Latn transform, whose main body entries are just the transforms using the second value of the 2-value kMandarin entries (it then calls Hani-Latn to handle any other characters). This ticket requests enhancing the existing tooling that generates the Han-Latin main body to also generate the Hant-Latn main body. We do not need this until Unicode 17 or later, after kMandarin updates including those in L2/25-029 have been incorporated.