Fix unhiding in IE11 (facebook#14126)

Setting to null isn't correct; setting to '' is. I opted to use dangerousStyleValue for consistency with the main path that we set things.

Fixes facebook#14114.

Test Plan:
Verified setting to '' works in Chrome and IE11. (Setting to null works in Chrome but not in IE11.)

Author: sophiebits

packages/react-dom/src/client/ReactDOMHostConfig.js

@@ -35,6 +35,7 @@ import {
   DOCUMENT_NODE,
   DOCUMENT_FRAGMENT_NODE,
 } from '../shared/HTMLNodeType';
+import dangerousStyleValue from '../shared/dangerousStyleValue';
 
 import type {DOMContainer} from './ReactDOM';
 
@@ -442,8 +443,7 @@ export function unhideInstance(instance: Instance, props: Props): void {
     styleProp.hasOwnProperty('display')
       ? styleProp.display
       : null;
-  // $FlowFixMe Setting a style property to null is the valid way to reset it.
-  instance.style.display = display;
+  instance.style.display = dangerousStyleValue('display', display);
 }
 
 export function unhideTextInstance(