Convert some CommonJS constructs to ES6

Summary:
Tried to automate this with [cjs-to-es6](https://github.com/nolanlawson/cjs-to-es6) but it only
works on vanilla JS files without any special Flow syntax. I converted some places
manually but we can just do the rest as we modify the files.

Reviewed By: jknoxville

Differential Revision: D16340187

fbshipit-source-id: b55c7ce2d719876e47e85f5f3fce13b8c8ae4010

src/ui/components/ButtonGroup.js

@@ -8,7 +8,7 @@
 import styled from '../styled/index.js';
 import {Component} from 'react';
 
-const PropTypes = require('prop-types');
+import PropTypes from 'prop-types';
 
 const ButtonGroupContainer = styled('div')({
   display: 'inline-flex',

src/ui/components/Tooltip.js

@@ -11,7 +11,7 @@ import type {TooltipOptions} from './TooltipProvider.js';
 import styled from '../styled/index.js';
 import {Component} from 'react';
 
-const PropTypes = require('prop-types');
+import PropTypes from 'prop-types';
 
 const TooltipContainer = styled('div')({
   display: 'contents',

src/ui/components/TooltipProvider.js

@@ -9,7 +9,7 @@ import styled from '../styled/index.js';
 import {colors} from './colors.js';
 import {Component} from 'react';
 
-const PropTypes = require('prop-types');
+import PropTypes from 'prop-types';
 
 const defaultOptions = {
   backgroundColor: colors.blueGrey,

src/ui/components/data-inspector/utils.js

@@ -5,7 +5,7 @@
  * @format
  */
 
-const naturalCompare = require('string-natural-compare');
+import naturalCompare from 'string-natural-compare';
 
 export function getSortedKeys(obj: Object): Array<string> {
   return Object.keys(obj).sort(naturalCompare);

src/ui/components/table/TableHead.js

@@ -23,7 +23,7 @@ import {colors} from '../colors.js';
 
 import FlexRow from '../FlexRow.js';
 
-const invariant = require('invariant');
+import invariant from 'invariant';
 
 type MenuTemplate = Array<MenuItemConstructorOptions>;