Changes

Summary

1. merged
2. suppress OCaml icons: avoid conflict of .ml and .ML, due to case-insensitive file-names in VSCode;
3. fix handling of lambdas in reconstruction of eq_congruent
4. more robust: avoid breakdown of Search dialog;
5. tuned;
6. always use Isabelle encoding, as in Isabelle/jEdit;
7. tuned signature;
8. clarified signature: more uniform ts vs. Scala;
9. discontinued isabelle_filesystem (superseded by isabelle_encoding), see also da1108a6d249; discontinued special treatment of workspace_dir as session directory;