Add Wacom tablet support for Cocoa

Task-number: QTBUG-25867
Change-Id: I48178b8913224ac8e907d42f57620947df12e930
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>
QHeaderView - reduce memory usage

Though the worst case memory usage was improved in
b800d8b94a7861ecf8853621f6556fca186fb5b7 the best case usage changed.

Since best case is the same as worst case in Qt5, we should
use as little as possible, which this patch ensures.

We reduce the memory usage from 3 to 2 ints per section - which is
half of worst case in Qt4. There seems to be no bigger cost in
performance doing that. The recalcSectionStartPos is still very fast.

This patch limits the maximum section size to (2^20) ~ 1.000.000 pixels.

This alleviates
Task-number: QTBUG-32325

Change-Id: I9b7530030a31b4e35cf1ca9e32c6b936f5ea9790
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>