Merge QStyleOption*V{2,3,4} classes together

Merge QStyleOption*V{2,3,4} classes together

In order to keep binary compatibility, Qt 4 introduced V{2,3,4}
classes for QStyleOption subclasses. They're simple, low level
containers for various members with public access (no accessors
required).

In Qt 5.0 we can break BC, so this patch moves the members
from the derived classes into the ``base'' ones.
The ``base'' ones get a version bump matching the highest
version available, and the V{2,3,4} classes become typedefs.

This change can cause problems in code that used QStyleOption
directly, especially QStyleOptionViewItem, because the old V4
fields get default initialization but the QStyle subclasses
detect that the option is a V4 option and expect all fields
to be properly initialized. The fix in such places is to
properly initialize all fields.

Task-number: QTBUG-23522
Change-Id: I2f782da09ca5cc8c4cbafc07448fb0d33153a251
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>