Summary:
If a modal window is near some of screen edges, it will be distorted
in undesired way when it's being animated.
In order to keep perspective distortions invariant, no matter where
the modal window is on the screen, we have to move that modal window
to the origin, scale it, rotate it, translate it, apply perspective projection,
and then move it back.
Test Plan:
* Opened Kate
* Opened "Open File" dialog (during the in animation, it was distorted as expected)
* Closed that dialog (during the out animation, it was distorted as expected)
Reviewers: #kwin, davidedmundson
Reviewed By: #kwin, davidedmundson
Subscribers: davidedmundson, kwin
Tags: #kwin
Differential Revision: https://phabricator.kde.org/D14687
fb4dc9a9cf