perf(ngBind): set textContent rather than using element.text()

"Speeds up chrome with ~10% firefox by ~5%"

We don't really see this result in benchmarks (https://www.dropbox.com/s/76wxqbvduade52s/big_table_benchmark_b1ee5396_vs_d580a954.zip?dl=0)
However, it's basically harmless.

Side effects:

Use strict equality check for `undefined` to replace with empty string. Most target browsers will output `undefined` rather than the empty
string if we don't do this. Previously, ngBindTemplate did not perform this check. However the change has been made to make behaviour
consistent across all target browsers (chrome does output the empty string).

Closes #9369
Closes #9396

src/ng/directive/ngBind.js

@@ -58,11 +58,9 @@ var ngBindDirective = ['$compile', function($compile) {
       $compile.$$addBindingClass(templateElement);
       return function ngBindLink(scope, element, attr) {
         $compile.$$addBindingInfo(element, attr.ngBind);
+        element = element[0];
         scope.$watch(attr.ngBind, function ngBindWatchAction(value) {
-          // We are purposefully using == here rather than === because we want to
-          // catch when value is "null or undefined"
-          // jshint -W041
-          element.text(value == undefined ? '' : value);
+          element.textContent = value === undefined ? '' : value;
         });
       };
     }
@@ -128,8 +126,9 @@ var ngBindTemplateDirective = ['$interpolate', '$compile', function($interpolate
       return function ngBindTemplateLink(scope, element, attr) {
         var interpolateFn = $interpolate(element.attr(attr.$attr.ngBindTemplate));
         $compile.$$addBindingInfo(element, interpolateFn.expressions);
+        element = element[0];
         attr.$observe('ngBindTemplate', function(value) {
-          element.text(value);
+          element.textContent = value === undefined ? '' : value;
         });
       };
     }