Update ActivityIndicator size prop type

Summary:
This diff updates the flow types for the ActivityIndicator size prop.

The android component [here](diffusion/FBS/browse/master/xplat/js/react-native-github/ReactAndroid/src/main/java/com/facebook/react/views/progressbar/ReactProgressBarViewManager.java$31-30) does not use a size prop

The iOS component [here](diffusion/FBS/browse/master/xplat/js/react-native-github/React/Fabric/Mounting/ComponentViews/ActivityIndicator/RCTActivityIndicatorViewComponentView.mm;e82762cefe5cddad4a7e8144c42c76eb4d907e56$14-15,23) uses the size prop, but only for small/large, not for the number type

Reviewed By: TheSavior

Differential Revision: D14247432

fbshipit-source-id: 43b74574548eaf97f96d68c18ed627465fd5e133

Author: rickhanlonii

Libraries/Components/ActivityIndicator/ActivityIndicator.js

@@ -70,15 +70,18 @@ type Props = $ReadOnly<{|
  * See http://facebook.github.io/react-native/docs/activityindicator.html
  */
 const ActivityIndicator = (props: Props, forwardedRef?: any) => {
-  const {onLayout, style, ...restProps} = props;
+  const {onLayout, style, size, ...restProps} = props;
   let sizeStyle;
+  let sizeProp;
 
-  switch (props.size) {
+  switch (size) {
     case 'small':
       sizeStyle = styles.sizeSmall;
+      sizeProp = 'small';
       break;
     case 'large':
       sizeStyle = styles.sizeLarge;
+      sizeProp = 'large';
       break;
     default:
       sizeStyle = {height: props.size, width: props.size};
@@ -89,6 +92,7 @@ const ActivityIndicator = (props: Props, forwardedRef?: any) => {
     ...restProps,
     ref: forwardedRef,
     style: sizeStyle,
+    size: sizeProp,
     styleAttr: 'Normal',
     indeterminate: true,
   };

Libraries/Components/ActivityIndicator/RCTActivityIndicatorViewNativeComponent.js

@@ -46,7 +46,7 @@ type NativeProps = $ReadOnly<{|
    *
    * See http://facebook.github.io/react-native/docs/activityindicator.html#size
    */
-  size?: ?(number | 'small' | 'large'),
+  size?: ?('small' | 'large'),
 
   style?: ?ViewStyleProp,
   styleAttr?: ?string,