Modernize the Player example

Fixed memory leak.
Renamed members, avoided passing args by copy.
Changed the style of member initialization.
Changed 0 to nullptr.
Changed to new signal/slot style if possible.
Removed Q_WS_SIMULATOR ifdef.
Changed signal/slot connection style.

Task-number: QTBUG-60627
Change-Id: I85bd6e56fe87f4e17f3c9964d6d1fdcb8202c519
Reviewed-by: Christian Stromme <christian.stromme@qt.io>