feat: Add instrumentation for React Router v3

[AbhiPrasad]

Just making my contribution to what will soon be the biggest yarn.lock file ever 😎

This PR adds instrumentation support for react-router v3. This is based entirely on the excellent getsentry/sentry implementation. To see how it works, see below:

// Must be `react-router` >= v3.2.0 and < 4.0.0
import * as Router from 'react-router';
import { reactRouterV3Instrumentation  } from '@sentry/react';

// Rendered below
const routes = (
  <Route />
  <Route />
  <Route />
);

// Have to generate PlainRoutes from routes
const appRoutes = Router.createRoutes(routes);

Sentry.init({
  tracesSampleRate: 1,
  integrations: [
    new Integrations.BrowserTracing({
      routingInstrumentation: reactRouterV3Instrumentation(Router.browserHistory, appRoutes, Router.match),
    });
  ]
});

If you notice, we make the user pass in a history, routes and Router.match. This is so that is is easier to test, can accommodate various history settings (hashRouting, browserRouting) and we don't make any assumptions on dependencies.

This is tested on Sentry and unit tested.

File	% Stmts	% Branch	% Funcs	% Lines	Uncovered Line #s
All files	93.18	89.19	100	92.5
reactrouter.tsx	93.18	89.19	100	92.5	100,105,119

[github-actions]

size-limit report

Path	Size	Loading time (3g)	Running time (snapdragon)	Total time
@sentry/browser - CDN Bundle (gzipped)	17.64 KB (+0.01% 🔺)	353 ms (+0.01% 🔺)	409 ms (-27.24% 🔽)	762 ms
@sentry/browser - Webpack	18.39 KB (0%)	368 ms (0%)	873 ms (+24.66% 🔺)	1.3 s
@sentry/react - Webpack	18.39 KB (0%)	368 ms (0%)	860 ms (+40.02% 🔺)	1.3 s
@sentry/browser + @sentry/tracing - CDN Bundle (gzipped)	22.57 KB (0%)	452 ms (0%)	367 ms (-5.66% 🔽)	818 ms

[getsentry-bot]

	Warnings
⚠️	Please add a changelog entry for your changes.

	Messages
📖	@sentry/browser bundle gzip'ed minified size: (ES5: 17.2363 kB) (ES6: 16.3525 kB)
📖	✅ TSLint passed

Generated by 🚫 dangerJS against bd89da7

[HazAT]

Looks solid :)