[Qt] The WebView should be flickable only using touch events

[Qt] The WebView should be flickable only using touch events
https://bugs.webkit.org/show_bug.cgi?id=100964

Reviewed by Kenneth Rohde Christiansen.

Let a user interacting with the WebView using a mouse the same way that a
desktop browser would.
This allows normal behaviors like text selecting, hover events, mouse cursors
as well as avoid touch highlighting and touch adjustment.

To do so we let all mouse events to be handled by the page directly instead
of sending them to QtWebPageEventHandler. Since unhandled mouse events aren't
pushed back to the PageClient like touch events does, this have the intended
behavior of not letting mouse events affect QQuickFlickable.

* UIProcess/API/qt/qquickwebview.cpp:
* UIProcess/API/qt/qquickwebview_p_p.h:
(QQuickWebViewFlickablePrivate):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@136119 268f45cc-cd09-0410-ab3c-d52691b4dbfc