AX: Make SVG Group containers accessible elements

AX: Make SVG Group containers accessible elements
https://bugs.webkit.org/show_bug.cgi?id=113939

Reviewed by Simon Fraser.

Source/WebCore:

SVG group containers are currently not exposed in the AX tree.
When an SVG element has a <title> child, that is not being used for the AX label.
When hit-testing, from Accessibility, SVG groups are never returned.

All these issues are fixed for Mac and iOS.
There are two tests because right now iOS skips all the top-level accessibility tests
due to fundamental architectural differences.

Tests: accessibility/svg-group-element-with-title.html
       platform/iphone-simulator/accessibility/svg-group-element-with-title.html

* accessibility/AccessibilityNodeObject.cpp:
(WebCore::AccessibilityNodeObject::alternativeText):
(WebCore::AccessibilityNodeObject::accessibilityDescription):
* accessibility/AccessibilityRenderObject.cpp:
(WebCore::AccessibilityRenderObject::accessibilityHitTest):
(WebCore::AccessibilityRenderObject::determineAccessibilityRole):
* accessibility/ios/WebAccessibilityObjectWrapperIOS.mm:
(-[WebAccessibilityObjectWrapper isSVGGroupElement]):
(-[WebAccessibilityObjectWrapper determineIsAccessibilityElement]):
(-[WebAccessibilityObjectWrapper accessibilityClickPoint]):
* rendering/HitTestRequest.h:
    Add a new option, AccessibilityHitTest, that will allow us to override normal behavior.
* rendering/svg/RenderSVGContainer.cpp:
(WebCore::RenderSVGContainer::nodeAtFloatPoint):
   Allow a SVG group to be the node at a point, for accessibility hit tests.

Tools:

Implement axController.elementAtPoint for iOS.
Implement a correct version of clickPoint for iOS.

* DumpRenderTree/ios/AccessibilityControllerIOS.mm:
(AccessibilityController::elementAtPoint):
* DumpRenderTree/ios/AccessibilityUIElementIOS.mm:
(AccessibilityUIElement::clickPointX):
(AccessibilityUIElement::clickPointY):

LayoutTests:

* accessibility/svg-group-element-with-title-expected.txt: Added.
* accessibility/svg-group-element-with-title.html: Added.
* platform/iphone-simulator/accessibility/svg-group-element-with-title-expected.txt: Added.
* platform/iphone-simulator/accessibility/svg-group-element-with-title.html: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@147802 268f45cc-cd09-0410-ab3c-d52691b4dbfc