[RNMobile] Enable Dismiss on PlainText in Android (#20095)

* Add flag for determining if running on Android

* Enable Dismiss button on PlainText. Enable show keyboard in Android on PlainText mount

* Enable Dismiss button on PlainText. Enable show keyboard in Android on PlainText mount

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

@@ -16,25 +16,39 @@ import styles from './style.scss';
 export default class PlainText extends Component {
 	constructor() {
 		super( ...arguments );
-		this.isIOS = Platform.OS === 'ios';
+		this.isAndroid = Platform.OS === 'android';
 	}
 
 	componentDidMount() {
 		// if isSelected is true, we should request the focus on this TextInput
-		if (
-			this._input.isFocused() === false &&
-			this._input.props.isSelected === true
-		) {
-			this.focus();
+		if ( this._input.isFocused() === false && this.props.isSelected ) {
+			if ( this.isAndroid ) {
+				/*
+				 * There seems to be an issue in React Native where the keyboard doesn't show if called shortly after rendering.
+				 * As a common work around this delay is used.
+				 * https://github.com/facebook/react-native/issues/19366#issuecomment-400603928
+				 */
+				this.timeoutID = setTimeout( () => {
+					this._input.focus();
+				}, 100 );
+			} else {
+				this._input.focus();
+			}
 		}
 	}
 
 	componentDidUpdate( prevProps ) {
-		if ( ! this.props.isSelected && prevProps.isSelected && this.isIOS ) {
+		if ( ! this.props.isSelected && prevProps.isSelected ) {
 			this._input.blur();
 		}
 	}
 
+	componentWillUnmount() {
+		if ( this.isAndroid ) {
+			clearTimeout( this.timeoutID );
+		}
+	}
+
 	focus() {
 		this._input.focus();
 	}