Attempt to make the positioning test of QWindow more reliable

The part of the test that verifies that setFramePosition moves the window
successfully appears to be very unreliable in the CI system. The "tested"
frame position is calculated to be at (40, 40) relative to the top left
of the available screen geometry, which can be non-zero due to task bars
and similar system ui elements. However that position appears to be
unreliable in the sense that the window manager doesn't seem to always
respect that. So instead let's try placing the window (by frame position)
in the center of the screen instead.

Change-Id: I96fe6c37e748fc18262632b5effe5a9e90dc0028
Reviewed-by: Jørgen Lind <jorgen.lind@theqtcompany.com>
Windows: Limit cursor cache.

Prevent the cursor cache from growing indefinitely hitting GDI resource
limits if new pixmap cursors are created repetitively by purging out
all-noncurrent pixmap cursors.

Change-Id: I4a3bbd6235af13e306ca84ac6fea3fcd69d53279
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>
Do not initialize accessibility code by default on startup.

Instead listen for if the accessibility service is running or not by
implementing AccessibilityStateChangeListener.
This seems to work smoothly when turning on or off TalkBack.

This should also improve startup time.

Change-Id: I3eb7d6cb9c9c1618afbb59675e4e089c9159019c
Reviewed-by: Christian Stromme <christian.stromme@theqtcompany.com>
qimage_conversions.cpp: Fix build on big endian systems

Change-Id: I8149eb2deaa101daf85a957ff48c3a7140c43bbc
Reviewed-by: Timo Jyrinki <timo.jyrinki@canonical.com>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@theqtcompany.com>
Android: Make cursor keys work again

On Android, we disable mouse selection, since that does not work
well with touch screens. In change a03a69efb9ed89cd4a90878eda20,
we accidentally disabled keyboard selection as well. Unfortunately,
disabling keyboard selection will disable all keyboard movement.
This change re-enables TextSelectableByKeyboard.

Task-number: QTBUG-42991
Change-Id: Ie63ed3d88a0abcb72f04e0ec60a5b91c0b14a47e
Reviewed-by: Christian Stromme <christian.stromme@theqtcompany.com>