D28224: Improve tests behaviour on set ups with high dpi

apol created this revision.
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REVISION SUMMARY
  We are testing on a 100x100 mock display. We'd ask QWidget for our
  display's dpi, it would not use the mock display but the actual
  system's. On my system it made the corners overlap with each other and
  all sorts of weird things happened.

TEST PLAN
  The tests actually pass here.

REPOSITORY
  R108 KWin

REVISION DETAIL
  https://phabricator.kde.org/D28224

AFFECTED FILES
  gestures.cpp
  screenedge.cpp
  screens.cpp
  screens.h

To: apol, #kwin
Cc: kwin, Orage, cacarry, LeGast00n, The-Feren-OS-Dev, cblack, jraleigh, zachus, fbampaloukas, GB_2, mkulinski, ragreen, jackyalcine, iodelay, crozbo, bwowk, ZrenBot, ngraham, alexeymin, himcesjf, lesliezhai, ali-mohamed, hardening, romangg, jensreuterberg, abetts, sebas, apol, ahiemstra, mart