[gtk] (20 commits) ...Merge branch 'wip/otte/dnd' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  5a726bc... drop: Add a state machine for tracking events (*)
  762c460... wayland: Destroy the offer on gdk_drop_finish() (*)
  8d2ed36... contentprovider: Add gdk_content_provider_new_typed() (*)
  dbad440... testdnd3: Use GValue dnd (*)
  da83457... dnd: Remove gdk_content_provider_new_with_callback() (*)
  e1f8c14... dnd: simplify code (*)
  3a7e3cf... dragdest: Simplify function (*)
  91d91a2... colorbutton, colorswatch: Simplify DND (*)
  80ba7fd... dragdest: Make gtk_drop_target_new() args be transfer full (*)
  f5e3584... placessidebar: Don't claim to support text dnd (*)
  9a7607b... contentprovider: Add a union content provider (*)
  e25bfa6... dragdest: Handle NULL content formats everywhere (*)
  9703fcc... notebook: Move dnd scrolling via arrows to own drop target (*)
  27d7aa1... notebook: Use proper DND (*)
  1145da3... placessidebar: Modernize DND (*)
  b8cf7ea... dnd: Port the TreeModel machinery to GValue DND (*)
  7ae5fd3... tests: Modernize testdnd2 (*)
  7ca149f... Remove gdk_content_provider_new_with_formats() (*)
  0d4d4e9... colorbutton: Fix drag source (*)
  03ee422... Merge branch 'wip/otte/dnd' into 'master'

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