[gtk] (16 commits) ...Merge branch 'wip/baedert/for-master' into 'master'

[Matthias Clasen <matthiasc src gnome org>]

Summary of changes:

  bf24da0... inspector: Add a type check (*)
  954a144... mediastream demo: Add a weak pointer to the window (*)
  0822de1... textview: Only show "insert emoji" menu item if editable (*)
  ebaea07... inspector: Avoid some failing casts (*)
  547842e... window: Keep titlebar after main child (*)
  76f2396... popover: Use gtk_widget_add_css_class (*)
  b37b853... adwaita: Reset popover background in backdrop (*)
  f5af187... listbox: Add _append (*)
  2f65459... stack: Only compare page names if the new page has one (*)
  b489a1f... stack: Allow NULL names (*)
  e976825... button: Use g_object_notify_by_pspec() (*)
  65b79d2... Avoid refering to old GtkContainer API in the docs (*)
  415946e... togglebutton: Modernice source file (*)
  f716daa... aboutdialog: Fix a code sample (*)
  41b458f... Fix and improve various code samples (*)
  0b2833f... Merge branch 'wip/baedert/for-master' into 'master'

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