Summary:
When `RCTGetExecutorID` was a static function in the header file, it would return nil when the app was running with ASan enabled even though directly calling `objc_getAssociatedObject(executor, RCTJavaScriptExecutorID)` returned the correct ID as an NSNumber. Moving this function into the .m file fixes this issue.
Closes https://github.com/facebook/react-native/pull/1712
Github Author: James Ide <ide@jameside.com>
Test Plan: Run the UIExplorer with ASan enabled in Xcode 7. Before this diff, the app would just hang since the executor was unable to read a valid ID and so it would bail out from running JS. With this diff the executor runs the JS and the UIExplorer works fine.
