[Qt] Use QQuickFlickable::setPixelAligned instead of doing pixel-alignment when rende...

[Qt] Use QQuickFlickable::setPixelAligned instead of doing pixel-alignment when rendering.
https://bugs.webkit.org/show_bug.cgi?id=83770

Reviewed by Kenneth Rohde Christiansen.

Source/WebCore:

Revert the previous way of dealing with things. The problem is that different layers
would end up rounding in different directions, and would cause jittering between
layers or with the QQuickWebPage's background.

* platform/graphics/texmap/TextureMapperGL.cpp:
(WebCore::TextureMapperGL::drawTexture):

Source/WebKit2:

- Do the alignment on the highest level as possible: the QQuickFlickable content item
  position. It already supports this with setPixelAligned which rounds the content item's position.
- Also move the setClip(true) to the common constructor as this constructor is currently only used by WTR.
- Remove setFlags(QQuickItem::ItemClipsChildrenToShape) as it is redundant with setClip(true).

* UIProcess/API/qt/qquickwebview.cpp:
(QQuickWebViewPrivate::QQuickWebViewPrivate):
(QQuickWebView::QQuickWebView):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@114118 268f45cc-cd09-0410-ab3c-d52691b4dbfc