Make the inline platform transform support string keys

Summary:
This diff makes the platform inline transformer support string keys, for example:

```
Platform.select({
  'ios': 'ios',
  'default': 'default',
});
```

This fixes https://github.com/facebook/metro/issues/134

Reviewed By: mjesun

Differential Revision: D7079013

fbshipit-source-id: 3e47bb4a28f2ac776475842982e089d5954d6521

packages/metro/src/JSTransformer/worker/__tests__/inline-test.js

@@ -186,6 +186,16 @@ describe('inline constants', () => {
     );
   });
 
+  it('inlines Platform.select in the code when using string keys', () => {
+    const code = `function a() {
+      var a = Platform.select({'ios': 1, 'android': 2});
+    }`;
+    const {ast} = inline('arbitrary.js', {code}, {platform: 'android'});
+    expect(toString(ast)).toEqual(
+      normalize(code.replace(/Platform\.select[^;]+/, '2')),
+    );
+  });
+
   it('replaces Platform.select in the code if Platform is a top level import', () => {
     const code = `
       var Platform = require('Platform');

packages/metro/src/JSTransformer/worker/inline.js

@@ -49,7 +49,17 @@ const isDev = (node, parent, scope) =>
   !t.isMemberExpression(parent);
 
 function findProperty(objectExpression, key, fallback) {
-  const property = objectExpression.properties.find(p => p.key.name === key);
+  const property = objectExpression.properties.find(p => {
+    if (t.isIdentifier(p.key) && p.key.name === key) {
+      return true;
+    }
+
+    if (t.isStringLiteral(p.key) && p.key.value === key) {
+      return true;
+    }
+
+    return false;
+  });
   return property ? property.value : fallback();
 }