Changes

Summary

1. provide Isabelle/jEdit plugins as services, and thus allow user components do the same;
2. merged
3. updated for release;
4. misc tuning for release;
5. update dependency;
6. trim whitespace;
7. misc tuning for release;
8. misc tuning for release;
9. isabelle build_components -u;
10. updated to Haskell Stach lts-18.12 with GHC ghc-8.10.7;
11. updated to current Cygwin, near 3.2.0; discontinued perl;
12. updated to sumatra_pdf-3.3.3;
13. updated default version;
14. updated to xz-java-1.9;
15. updated to sqlite-jdbc-3.36.0.3;
16. updated to postgresql-42.2.24;
17. updated to jfreechart-1.5.3;
18. updated to flatlaf-1.6;
19. clarified signature;
20. clarified Term.dest_abs (again, refining 71dfb835025d): only Free names are relevant for abstract terms, without syntax;
21. clarified sledgehammer_provers, following d8dc8fdc46fc;
22. proper term operation Term.dest_abs;
23. tuned, following Syntax_Trans.variant_abs;
24. proper patterns for (- numeral t), amending 03ff4d1e6784;
25. tuned;