Clean up multiple RenderedPosition::absoluteRect definitions and correct LayoutUnit...

Clean up multiple RenderedPosition::absoluteRect definitions and correct LayoutUnit usage
https://bugs.webkit.org/show_bug.cgi?id=83604

Reviewed by Julien Chaffraix.

Removing unnecessary definitions of absoluteRect and replacing them with a single public
version that's more explicit about its contract.

Also correcting a LayoutUnit misuse, as rects in absolute coordinates should be returned
using integers, not LayoutUnits. See https://trac.webkit.org/wiki/LayoutUnit for details.

No new tests. No change in behavior.

* editing/Editor.cpp:
(WebCore::Editor::firstRectForRange):
* editing/RenderedPosition.cpp:
(WebCore::RenderedPosition::absoluteRect): Pixel snapping the local rect before converting
to absolute coordinates.
* editing/RenderedPosition.h:
(RenderedPosition):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@113792 268f45cc-cd09-0410-ab3c-d52691b4dbfc