Prefer QPA implementation in qsystemtrayicon_x11 if available

In order to have the possibility to provide a custom QSystemTrayIcon
implementation in the platform theme instead of the X11 xembed based
one, the qpa implementation needs to be called. This was not possible
as qpa and x11 implementation were compile time mutual exclusive.

This change moves the qpa implementation in the shared part and the
methods in qsystemtrayicon_qpa just delegate to them. In addition the
_x11 part tries to create a QPlatformSystemTrayIcon through the
platform theme and if that succeeds the implementation prefers the qpa
variant and delegates to the same methods.

Change-Id: I6b33acac63524a77ebdce39af6eb74666f8c7561
Reviewed-by: Kevin Krammer <kevin.krammer@kdab.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
Doc: Correct typos in QModelIndex::internalId() documentation

Change-Id: Iea2fd83764711889b828997d56b9f7dcdbdd75fb
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>
Improve error reporting in selftests of testlib.

Output the file name and fix line number to be 1..n.

Change-Id: I3ba7f84b99ce3664bc3e403b230307511b15fe1f
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>
QtCore: Fix MSVC 64bit warnings about conversion from size_t to int.

warning C4267: '=' : conversion from 'size_t' to 'int', possible loss of data

Change-Id: I9be380cbb7bed4cd95515074c7cad7e41a511dc9
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@digia.com>