Improve file handling. Add test for roundtrip. #47

Job	Run time
build (21, adopt, macos-latest)	6m 17s
build (21, adopt, ubuntu-latest)	3m 56s
build (21, adopt, windows-latest)	5m 19s
build (21, adopt-openj9, macos-latest)	6m 37s
build (21, adopt-openj9, ubuntu-latest)	5m 10s
build (21, adopt-openj9, windows-latest)	5m 45s
build (21, corretto, macos-latest)	6m 10s
build (21, corretto, ubuntu-latest)	4m 21s
build (21, corretto, windows-latest)	5m 9s
build (21, dragonwell, ubuntu-latest)	3m 57s
build (21, dragonwell, windows-latest)	5m 7s
build (21, liberica, macos-latest)	5m 58s
build (21, liberica, ubuntu-latest)	4m 6s
build (21, liberica, windows-latest)	5m 9s
build (21, microsoft, ubuntu-latest)	4m 28s
build (21, microsoft, windows-latest)	5m 5s
build (21, temurin, macos-latest)	6m 36s
build (21, temurin, ubuntu-latest)	4m 12s
build (21, temurin, windows-latest)	4m 39s
build (21, zulu, macos-latest)	7m 21s
build (21, zulu, ubuntu-latest)	4m 37s
build (21, zulu, windows-latest)	5m 7s
	1h 55m 6s

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