[RNMobile] Make placeholder text working on RichText (#13699)

* Make placeholder text working again on RichText

* Make sure the native side is always refreshed when the RichText component is cleared

* Remove placeholder check

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

@@ -360,7 +360,12 @@ export class RichText extends Component {
 			} ) );
 
 		// Save back to HTML from React tree
-		const html = '<' + tagName + '>' + value + '</' + tagName + '>';
+		let html = '<' + tagName + '>' + value + '</' + tagName + '>';
+		// We need to check if the value is undefined or empty, and then assign it properly otherwise the placeholder is not visible
+		if ( value === undefined || value === '' ) {
+			html = '';
+			this.lastEventCount = undefined; // force a refresh on the native side
+		}
 
 		return (
 			<View>
@@ -373,6 +378,7 @@ export class RichText extends Component {
 					}
 					}
 					text={ { text: html, eventCount: this.lastEventCount } }
+					placeholder={ this.props.placeholder }
 					onChange={ this.onChange }
 					onFocus={ this.props.onFocus }
 					onBlur={ this.props.onBlur }