Fix TextField::placeholderText docs

For usability reasons the placeholder text is kept always visible when
the control is empty, even when focused.

Task-number: QTBUG-36303
Change-Id: I79733b0cf2a48807fb45d5697399f183c2b97f94
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
Remove unused white rectangle causing drawing issues

The spinbox has a white rectangle which overlaps the frames with some
styles (eg. oxygen). However the Rectangle itself serves no real purpose
and so it's removed.

Change-Id: I37a6862dfd8ac21fb24b54261fa7d7ab54aa23c7
Reviewed-by: David Edmundson <davidedmundson@kde.org>
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>
Fix implicit width for SpinBox

This patch ensures that we take the minimum width of the SpinBox
into account when getting the size from the style item.

The patch still relies on the height of the TextField since we
want to ensure that they keep similar height and the existing
spinbox code behaves somewhat erratic.

Task-number: QTBUG-36283
Change-Id: I50d14e5afb2576548c381e7f70063dfcb727e7d6
[ChangeLog][QtQuickControls]Fixed implicit width for SpinBox
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>
Fix StackView documentation

The extra "property Component" breaks the examples.

Task-number: QTBUG-35864
Change-Id: I1317f9a2ce42f4d9e4a03ecc3b85286b1eb3e855
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
Controls: Fixed support for Keys attached property on controls allowing text input

By forwarding key events from the internal control.

It includes TextField, TextArea, ComboBox, SpinBox. The key events from
internal are Keys.forwardTo controls, then user could customize their
own behavior for those controls.

Autotest are included.

[ChangeLog][QtQuickControls] Fixed support for Keys attached property on
controls allowing text input, by forwarding key events from the internal
control.

Task-number: QTBUG-33493
Task-number: QTBUG-34101
Task-number: QTBUG-35763
Change-Id: I00ea131160e55048b34fe0713e1ee02ff9472f05
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>