Switch: useMergeRef for forwarding ref

Summary:
Changelog:
[Internal] - Replace `useImperativeHandle` usage with new `useMergeRef` which will keep both the forwarded and internal ref handle up to date (in case the instance ever changes). That being said, this change was not motivated in fear of a stale ref but more an intention to show that `useImperativeHandle`'s use case is more about creating a selective API and `useMergeRef` is better suited for publishing ref updates.

Reviewed By: yungsters

Differential Revision: D28950632

fbshipit-source-id: 594afda02693545aab77f24566180c338b58bb8b

Libraries/Components/Switch/Switch.js

@@ -12,6 +12,7 @@
 import Platform from '../../Utilities/Platform';
 import * as React from 'react';
 import StyleSheet from '../../StyleSheet/StyleSheet';
+import useMergeRefs from '../../Utilities/useMergeRefs';
 
 import AndroidSwitchNativeComponent, {
   Commands as AndroidSwitchCommands,
@@ -153,7 +154,8 @@ const SwitchWithForwardedRef: React.AbstractComponent<
   const nativeSwitchRef = React.useRef<React.ElementRef<
     typeof SwitchNativeComponent | typeof AndroidSwitchNativeComponent,
   > | null>(null);
-  React.useImperativeHandle(forwardedRef, () => nativeSwitchRef.current);
+
+  const ref = useMergeRefs(nativeSwitchRef, forwardedRef);
 
   const [native, setNative] = React.useState({value: null});
 
@@ -200,7 +202,7 @@ const SwitchWithForwardedRef: React.AbstractComponent<
         onChange={handleChange}
         onResponderTerminationRequest={returnsFalse}
         onStartShouldSetResponder={returnsTrue}
-        ref={nativeSwitchRef}
+        ref={ref}
       />
     );
   } else {
@@ -232,7 +234,7 @@ const SwitchWithForwardedRef: React.AbstractComponent<
         onChange={handleChange}
         onResponderTerminationRequest={returnsFalse}
         onStartShouldSetResponder={returnsTrue}
-        ref={nativeSwitchRef}
+        ref={ref}
       />
     );
   }