clarified Document_Editor.Session: more explicit types, more robust operations;
eliminated await_stable_snapshot in favour of delay_build;
#built-in components
src/Tools/jEdit
src/Tools/GraphBrowser
src/Tools/Graphview
src/Tools/Setup
src/Tools/VSCode
src/HOL/Mutabelle
src/HOL/Library/Sum_of_Squares
src/HOL/SPARK
src/HOL/Tools
src/HOL/TPTP