Restore bulk edit support for remarkup fields (description, add comment)

Summary:
Depends on D18866. Ref T13025. Fixes T12415. This makes the old "Add Comment" action work, and adds support for a new "Set description to" action (possibly, I could imagine "append description" being useful some day, maybe).

The implementation is just a `<textarea />`, not a whole fancy remarkup box with `[Bold] [Italic] ...` buttons, preview, typeaheads, etc. It would be nice to enrich this eventually but doing the rendering in pure JS is currently very involved.

This requires a little bit of gymnastics to get the transaction populated properly, and adds some extra validation since we need some code there anyway.

Test Plan:
  - Changed the description of a task via bulk editor.
  - Added a comment to a task via bulk editor.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13025, T12415

Differential Revision: https://secure.phabricator.com/D18867

webroot/rsrc/js/phuix/PHUIXFormControl.js

@@ -57,6 +57,9 @@ JX.install('PHUIXFormControl', {
         case 'text':
           input = this._newText(spec);
           break;
+        case 'remarkup':
+          input = this._newRemarkup(spec);
+          break;
         default:
           // TODO: Default or better error?
           JX.$E('Bad Input Type');
@@ -312,6 +315,28 @@ JX.install('PHUIXFormControl', {
       };
     },
 
+    _newRemarkup: function(spec) {
+      var attrs = {};
+
+      // We could imagine a world where this renders a full remarkup control
+      // with all the hint buttons and client behaviors, but today much of that
+      // behavior is defined server-side and thus this isn't a world we
+      // currently live in.
+
+      var node = JX.$N('textarea', attrs);
+      node.value = spec.value || '';
+
+      return {
+        node: node,
+        get: function() {
+          return node.value;
+        },
+        set: function(value) {
+          node.value = value;
+        }
+      };
+    },
+
     _newOptgroups: function(spec) {
       var value = spec.value || null;