This series of commits replaces the former approach of building custom extract files from CLDR .xml files and instead uses the .json files that CLDR now distributes. It involves data structure changes so is fairly involved; have broken down into a few separate commits.
New PR created from a branch so I could change a few things.
Instead of using custom-built PHP data files
To quote @stuwest from #7:
New PR created from a branch so I could change a few things.