TextInput: Remove PropTypes, NativeMethodsMixin; Convert to ES6 class (#21885)

Summary:
This pull requests converts `TextInput` to an ES6 class, and in the process removes its usage of `prop-types` and `NativeMethodsMixin`.

The code (and some relevant types) for the native components have been moved to `TextInputNativeComponent.js`.

The rest of the flow proptypes have been moved to `TextInputTypes.js`.
Pull Request resolved: https://github.com/facebook/react-native/pull/21885

Reviewed By: RSNara

Differential Revision: D10515754

Pulled By: TheSavior

fbshipit-source-id: 5cfb25344385904b37a49582008c2a4b46db809d

Libraries/Components/TextInput/TextInputNativeComponent.js

@@ -0,0 +1,64 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ * @format
+ */
+
+'use strict';
+
+const Platform = require('Platform');
+const ReactNative = require('ReactNative');
+
+const requireNativeComponent = require('requireNativeComponent');
+
+import type {Props} from 'TextInputTypes';
+
+let AndroidTextInput = null;
+let RCTMultilineTextInputView = null;
+let RCTSinglelineTextInputView = null;
+
+if (Platform.OS === 'android') {
+  AndroidTextInput = requireNativeComponent('AndroidTextInput');
+} else if (Platform.OS === 'ios') {
+  RCTMultilineTextInputView = requireNativeComponent(
+    'RCTMultilineTextInputView',
+  );
+  RCTSinglelineTextInputView = requireNativeComponent(
+    'RCTSinglelineTextInputView',
+  );
+}
+
+type NativeProps = $ReadOnly<{|
+  ...Props,
+  text?: ?string,
+  onSelectionChangeShouldSetResponder?: ?() => boolean,
+  mostRecentEventCount?: ?number,
+|}>;
+
+declare class TextInputType extends ReactNative.NativeComponent<NativeProps> {
+  /**
+   * Removes all text from the `TextInput`.
+   */
+  clear(): mixed;
+
+  /**
+   * Returns `true` if the input is currently focused; `false` otherwise.
+   */
+  isFocused(): boolean;
+}
+
+export type {TextInputType};
+
+module.exports = {
+  AndroidTextInput: ((AndroidTextInput: any): Class<TextInputType>),
+  RCTMultilineTextInputView: ((RCTMultilineTextInputView: any): Class<
+    TextInputType,
+  >),
+  RCTSinglelineTextInputView: ((RCTSinglelineTextInputView: any): Class<
+    TextInputType,
+  >),
+};