Changes

Summary

1. clarified exception: avoid odd compiler warning;
2. update to scala-3.2.1; enforce rebuild of Isabelle/ML + Isabelle/Scala;
3. recovered check from 69139cc01ba1: Windows does not support PosixFilePermission;
4. update to jdk-17.0.5 (Oct-2022);
5. more standard component build process;
6. proper treatment of tar.gz double-extension;
7. proper download, instead of assuming local directory;
8. more standard component build process;
9. clarified signature; omit somewhat pointless test for "unzip" command;
10. clarified signature; tuned messages;
11. discontinue unused JCEF: superseded by Electron with its bundled Chromium;
12. prefer deterministic result;