Fix animations in OSS debug builds by modifying Platform.isTesting() behaviour

Summary:
In D14244606 I "fixed" `Platform.isTesting()` in JS. By fixed, I made it return true when running SSTs.

People in OSS complained about this in discord and [github](facebook#27010). The problem is that this call returns true whenever an RN project references Detox in the build.gradle file. In practice, this has been really annoying, because it has disabled animations in debug builds, due to D13811035.

The fix is to be more specific, and look for the exact screenshot test activity. I haven't explicitly verified this doesn't trigger from Detox, but it shouldn't. I'll coordinate on the github issue to verify.

Changelog: [Android][Fixed] Fix animations in OSS debug builds by modifying `Platform.isTesting()` behaviour

Reviewed By: TheSavior

Differential Revision: D19384098

fbshipit-source-id: 22c885219f2c00f5dcc3b930b068bfd2ad7e4b8e

Author: Peter Argany

ReactAndroid/src/main/java/com/facebook/react/modules/systeminfo/AndroidInfoModule.java

@@ -93,7 +93,7 @@ public void invalidate() {}
 
   private Boolean isRunningScreenshotTest() {
     try {
-      Class.forName("android.support.test.rule.ActivityTestRule");
+      Class.forName("com.facebook.testing.react.screenshots.ReactAppScreenshotTestActivity");
       return true;
     } catch (ClassNotFoundException ignored) {
       return false;