D27975: Fix the tablet mode manager

bshah created this revision.
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REVISION SUMMARY
  Previously we connected the hasTabletModeSwitchChanged to the
  tabletModeAvailableChanged which meant that in startup once libinput
  signaled us that we have switch, we would toggle that we now have a
  tablet mode.
  
  But, we were connecting this to wrong signal, as a result tablet mode
  would become available, but actual tablet switch inputspy was never
  getting registered, so tablet mode events were silently ignored.

TEST PLAN
  tested on Dell Inspiron 7000 laptop where tablet mode switch
  is available

REPOSITORY
  R108 KWin

BRANCH
  bshah/fix-tablet-mode

REVISION DETAIL
  https://phabricator.kde.org/D27975

AFFECTED FILES
  tabletmodemanager.cpp

To: bshah
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