TextInput: Unified support of clearsOnBeginEditing prop

Summary: The implementation of `clearsOnBeginEditing` was unified and moved to superclass.

Reviewed By: javache

Differential Revision: D5299396

fbshipit-source-id: 98c5494a782cbe4df5b2d6021828eb7b2012f6dc

RNTester/js/TextInputExample.ios.js

@@ -684,6 +684,24 @@ exports.examples = [
               selectTextOnFocus={true}
             />
           </WithLabel>
+          <WithLabel label="clearTextOnFocus (multiline)">
+            <TextInput
+              placeholder="text is cleared on focus"
+              defaultValue="text is cleared on focus"
+              style={styles.default}
+              clearTextOnFocus={true}
+              multiline={true}
+            />
+          </WithLabel>
+          <WithLabel label="selectTextOnFocus (multiline)">
+            <TextInput
+              placeholder="text is selected on focus"
+              defaultValue="text is selected on focus"
+              style={styles.default}
+              selectTextOnFocus={true}
+              multiline={true}
+            />
+          </WithLabel>
         </View>
       );
     }