fix(ngAria): ensure boolean values for aria-hidden and aria-disabled

aria-hidden should mirror the boolean representation of their ng-*
counterpart (ng-show, ng-hide) instead of their actual value. Same
applies to aria-disabled and ng-disabled

Closes #11365

Author: fredsa

src/ngAria/aria.js

@@ -115,9 +115,8 @@ function $AriaProvider() {
       var ariaCamelName = attr.$normalize(ariaAttr);
       if (config[ariaCamelName] && !attr[ariaCamelName]) {
         scope.$watch(attr[attrName], function(boolVal) {
-          if (negate) {
-            boolVal = !boolVal;
-          }
+          // ensure boolean value
+          boolVal = negate ? !boolVal : !!boolVal;
           elem.attr(ariaAttr, boolVal);
         });
       }