[gnome-builder] (8 commits) ...Merge branch 'wip/chergert/libpanel-changes'

[Christian Hergert <chergert src gnome org>]

Summary of changes:

  e3f4226... libpanel: port to updated libpanel API (*)
  eafed4d... plugins/sessionui: add (incomplete) sessionui plugin (*)
  0c8b697... plugins/symbol-tree: give line/column in hover provider (*)
  1883d55... libide/editor: implement discard for page (*)
  f2cb289... libide/editor: handle save delegate close signal (*)
  faf0e5e... libide/gui: implement agree_to_close vfuncs (*)
  70c2209... libide/editor: implement agree_to_close vfuncs (*)
  b3ccad8... Merge branch 'wip/chergert/libpanel-changes'

(*) This commit already existed in another branch; no separate mail sent