Zoneinfo icu

This adds ICU timezone datafiles from icu-data repository.

The source .txt data files are sources for the binary .res files, which are compiled at build time. Shipping this enabled to update timezone database files at runtime for icu, by rebuilding icu by setting U_TIMEZONE_FILES_DIR build-time config option, or at runtime with environment variable ICU_TIMEZONE_FILES_DIR. This will resolve a long standing bug that tzdata inside icu is never updated, and thus apps that use icu to access tzdata are always out of date (i.e. php).

Note that the .txt files do duplicate tzdata data files a bit. As they are generated with a Java app by ICU upstream which merges tzdata files as input together with https://github.com/unicode-org/cldr xmls overrides. Maybe in the future, I will provide a more complete / reproducible process to rebuild icu input .txt files from the tzdata files directly with the xml overlays "from complete scratch".

However, at least .res files generated are reproducible and match checksums of the prebuild .res files distributed in the icu-data repository.