setWlSource will delete the X11Source while XToWlDrag did not
finish leading to potential crashes. Since it's only set when
creating a WlToXDrag, only remove it in this case.
We can also replace the virtual with a type check if we have to do
it anyways which also makes it clearer what is going on.
Once in a while, we receive complaints from other fellow KDE developers
about the file organization of kwin. This change addresses some of those
complaints by moving all of source code in a separate directory, src/,
thus making the project structure more traditional. Things such as tests
are kept in their own toplevel directories.
This change may wreak havoc on merge requests that add new files to kwin,
but if a patch modifies an already existing file, git should be smart
enough to figure out that the file has been relocated.
We may potentially split the src/ directory further to make navigating
the source code easier, but hopefully this is good enough already.
