[BlackBerry] Require text editable element to be enabled for VKB

[BlackBerry] Require text editable element to be enabled for VKB
https://bugs.webkit.org/show_bug.cgi?id=89876

Reviewed by Yong Li.

After bug 58837 got in, children of <fieldset> now can inherit the disabled
state of the fieldset. When trying for instance fast/forms/fieldset/fieldset-disabled.html,
it can be seen that when they are visually disabled, the input handling can still be triggered. So
add an extra check to isTextBasedContentEditableElement that the element is enabled.

Reviewed internally by Mike Fenton.

* WebKitSupport/DOMSupport.cpp:
(BlackBerry::WebKit::DOMSupport::isTextBasedContentEditableElement):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@121155 268f45cc-cd09-0410-ab3c-d52691b4dbfc