Add SPDX license (but not copyright) headers to all files which follow a
certain pattern in their existing non-machine-readable header comment.
This commit was entirely generated using the command:
```
git ls-files gio/*.[ch] | xargs perl -0777 -pi -e 's/\n \*\n \* This library is free software; you can redistribute it and\/or\n \* modify it under the terms of the GNU Lesser General Public/\n \*\n \* SPDX-License-Identifier: LGPL-2.1-or-later\n \*\n \* This library is free software; you can redistribute it and\/or\n \* modify it under the terms of the GNU Lesser General Public/igs'
```
Signed-off-by: Philip Withnall <pwithnall@endlessos.org>
Helps: #1415
This can be handy when you want to change the sense of a toggle
in the UI without rewriting the underlying logic. Currently, this
is just exposed as a construct-only property. We may add a
convenience wrapper or a special !property syntax for this later.
https://bugzilla.gnome.org/show_bug.cgi?id=728489
Add a new type of GAction that represents the value of a property on an
object. As an example, this might be used on the "visible-child-name"
property of a GtkStack.
https://bugzilla.gnome.org/show_bug.cgi?id=703270
