The main advantage of SPDX license identifiers over the traditional
license headers is that it's more difficult to overlook inappropriate
licenses for kwin, for example GPL 3. We also don't have to copy a
lot of boilerplate text.
In order to create this change, I ran licensedigger -r -c from the
toplevel source directory.
There are several ways to handle unmapping of a wl_surface. The first
one is to destroy the associated AbstractClient instance. The second one
is to transition the AbstractClient in a special state.
The problem with the second approach is that it makes animations such as
fade out more difficult to handle since effects in kwin are geared more
towards the first approach (destroying AbstractClient).