[effects/sheet] Modernize code

Summary:

• Use new connect syntax
• Fix coding style
• Port to TimeLine
• Delete unused includes
• Use interpolate helper
• Drop WindowInfo class

Behavior of this effect hasn't been changed.

Test Plan: Opened/closed an "Open File" dialog, it still flies in/out.

Reviewers: KWin, davidedmundson

Reviewed By: KWin, davidedmundson

Subscribers: davidedmundson, anthonyfieroni, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D14685