produce an uncompressed size report from a ZBI
usage: fx zbi-size-report [--zbi <file>] [--output-json <file>]
--zbi <file> path to ZBI to analyze; defaults to out/default/fuchsia.zbi
--output-json <file> where to save report of uncompressed file sizes
in a d3js-friendly format; defaults to a temporary file
bootfs-size-report source code