fix isOutputRedundant logic

Summary:
isOutputRedundant badly failed when two screens had
the exact same geometry (that should be, the base
case for "cloning" screens.
now the logic is:
a screen is redundant if:

• its geometry is contained in another one
• if their resolutions are different, the "biggest" one wins
• if they have the same geometry, the one with the lowest id wins (arbitrary, but gives reproducible behavior and makes the primary

BUG:375507

Test Plan:
tested with two screens:

• overlapping, same resolution: the lowest id (0, the primary) wins, the other one doesn't get a view
• overlapping, different resolutions: the biggest one wins
• not overlapping: both get a view

Reviewers: sebas, Plasma, davidedmundson

Reviewed By: Plasma, davidedmundson

Subscribers: davidedmundson, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D4309