Add Smart TV UX as device type
Summary: In light of the Plasma Bigscreen shell it seemed useful to have a device type for Smart TVs. The content is partially based on this post from Marco Martin: https://notmart.org/blog/2020/03/behind-plasma-bigscreen/
Some of the content is just a best-guess for the UX based on screenshots of Plasma Bigscreen. So some parts may need to be changed to better recommendations for an optimal UX.
Test Plan: I ran "make html" and verified the added content locally
Previously also submitted as Differential Revision: https://phabricator.kde.org/D28554