Implement console group APIs (#18555)
Implement console group APIs (#18555)

Summary:
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React Native provides an implementation of the Web "Console" API, which is a powerful mechanism for debugging and analyzing RN apps. However, one subset of the Console API that RN does not provide is the "grouping" functions, namely `console.group` and `console.groupEnd`. These functions provide a useful way to see how an application behaves within a different parts of an application hierarchy.

I modified the "RNTester" app to create a console group each time an example is tapped, and the group is ended when the "Back" button is tapped. Here is an example of the grouping as seen in the Xcode console.

<img width="651" alt="console grouping" src="https://user-images.githubusercontent.com/445421/37882070-d2ae7860-306d-11e8-8cf4-be843a864f43.png">

https://github.com/facebook/react-native-website/pull/270

[GENERAL] [ENHANCEMENT] [console.js] - Add `console.group()` and `console.groupEnd()` APIs, matching the Web Console API.
Closes https://github.com/facebook/react-native/pull/18555

Differential Revision: D7992131

Pulled By: hramos

fbshipit-source-id: 0d28896292563922240ae2100ed49e35b6d1f102

myntra/react-native,facebook/react-native,pandiaraj44/react-native,myntra/react-native,myntra/react-native,exponent/react-native,exponent/react-native,exponent/react-native,arthuralee/react-native,hammerandchisel/react-native,janicduplessis/react-native,hammerandchisel/react-native,arthuralee/react-native,hoangpham95/react-native,myntra/react-native,pandiaraj44/react-native,pandiaraj44/react-native,javache/react-native,exponent/react-native,javache/react-native,hoangpham95/react-native,janicduplessis/react-native,exponentjs/react-native,hammerandchisel/react-native,exponentjs/react-native,hoangpham95/react-native,hammerandchisel/react-native,exponentjs/react-native,exponent/react-native,pandiaraj44/react-native,janicduplessis/react-native,hoangpham95/react-native,hammerandchisel/react-native,javache/react-native,pandiaraj44/react-native,arthuralee/react-native,hammerandchisel/react-native,exponent/react-native,facebook/react-native,hoangpham95/react-native,exponentjs/react-native,facebook/react-native,facebook/react-native,myntra/react-native,facebook/react-native,arthuralee/react-native,hoangpham95/react-native,javache/react-native,myntra/react-native,myntra/react-native,janicduplessis/react-native,exponent/react-native,hoangpham95/react-native,janicduplessis/react-native,arthuralee/react-native,pandiaraj44/react-native,janicduplessis/react-native,janicduplessis/react-native,hoangpham95/react-native,facebook/react-native,exponentjs/react-native,javache/react-native,hammerandchisel/react-native,javache/react-native,javache/react-native,javache/react-native,exponentjs/react-native,hammerandchisel/react-native,janicduplessis/react-native,facebook/react-native,javache/react-native,pandiaraj44/react-native,myntra/react-native,exponent/react-native,exponentjs/react-native,facebook/react-native,pandiaraj44/react-native,myntra/react-native,exponentjs/react-native,facebook/react-native