Rework locale data filtering (-modern is going away)

[bojanz]

CLDR v45 deprecated the "modern" packages. Instead, we are expected to use the "full" packages and then filter locales based on the data in https://github.com/unicode-org/cldr-json/blob/main/cldr-json/cldr-core/coverageLevels.json

Reference: https://unicode-org.atlassian.net/browse/CLDR-16465

[Ishwarya-Selvaraj]

I would like to give it a try @bojanz