Remove focus from RichText when unmounting

In #15999 this behavior was changed to prevent the keyboard from disappearing
when you press Enter to create a new paragraph.

This worked in that case, but had the side effect of TextInputState still
thinking a dead view had focus, and causing a crash in some scenarios.

packages/block-editor/src/components/rich-text/index.native.js

@@ -702,7 +702,7 @@ export class RichText extends Component {
 
 	componentWillUnmount() {
 		if ( this._editor.isFocused() ) {
-			// this._editor.blur();
+			this._editor.blur();
 		}
 	}