Clone ObjectMethod before toExpression in preset

Summary:
The React Native Babel preset replaces `Platform.select({...})` with the selected property during production transforms. When the selected property is an object method, converting it to an expression mutates the node in place. Since the replacement is computed before the purity check, bailing out on an impure sibling leaves the mutated method behind, producing invalid output. Clone the method before converting it.

Also assess purity on the property itself: an `ObjectMethod` has no value, so checking the value treated every method as impure and skipped inlining.

## Changelog:

[GENERAL] [FIXED] - Fix Platform.select inlining producing invalid output for object methods when discarding impure initializers is skipped

Reviewed By: GijsWeterings

Differential Revision: D119305530

Author: vzaidman

packages/react-native-babel-preset/src/__tests__/inline-platform-plugin-test.js

@@ -493,6 +493,15 @@ describe('Platform.select', () => {
     `);
   });
 
+  test('does not mutate object methods when bailing out on impure initializers', () => {
+    expectUnchanged(`
+      const value = require('react-native').Platform.select({
+        ios() { return 1; },
+        android: sideEffect(),
+      });
+    `);
+  });
+
   test('does not inline computed keys', () => {
     expect(select('{[key]: 1, default: 2}')).toContain('Platform.select');
   });

packages/react-native-babel-preset/src/inline-platform-plugin.js

@@ -443,7 +443,9 @@ module.exports = function inlinePlatformPlugin(
         if (t.isObjectProperty(property)) {
           return property.value;
         }
-        return t.toExpression(property);
+        // Clone: toExpression mutates in place, e.g. `ios() {}` would be
+        // left mutated if the purity check below bails out.
+        return t.toExpression(t.cloneNode(property));
       }
     }
     return fallback();