AX: Implement ARIA 1.1 @aria-current on iOS

AX: Implement ARIA 1.1 @aria-current on iOS
https://bugs.webkit.org/show_bug.cgi?id=149297

Reviewed by Chris Fleizach.

Source/WebCore:

Added support for iOS to query for aria-current status.
Also, enabled aria-current.html test on iOS.

* accessibility/ios/WebAccessibilityObjectWrapperIOS.mm:
(-[WebAccessibilityObjectWrapper accessibilityInvalidStatus]):
(-[WebAccessibilityObjectWrapper accessibilityARIACurrentStatus]):
(-[WebAccessibilityObjectWrapper accessibilityMathRootIndexObject]):

Tools:

Added support to test aria-current on iOS.

* DumpRenderTree/ios/AccessibilityUIElementIOS.mm:
(AccessibilityUIElement::stringAttributeValue):
* WebKitTestRunner/InjectedBundle/ios/AccessibilityUIElementIOS.mm:
(WTR::AccessibilityUIElement::stringAttributeValue):

LayoutTests:

* platform/ios-simulator/TestExpectations:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@189994 268f45cc-cd09-0410-ab3c-d52691b4dbfc