Re-enable flow module checking

Summary:
Setting the module extension to .tsx overrode the defaults, meaning .js files were no longer being checked when imported.

This adds the defaults back to the extensions to be checked, including `.js`
It does seem to cause errors importing `.tsx` at the moment, but there aren't many so I've just $FlowFixMe'd them for now.

https://flow.org/en/docs/config/options/#toc-module-file-ext-string

Reviewed By: passy

Differential Revision: D16333800

fbshipit-source-id: 7bea92c038048234b4f634704f71c15d79ab3c63

.flowconfig

@@ -22,6 +22,10 @@ emoji=true
 all=true
 include_warnings=true
 module.name_mapper='flipper' -> '<PROJECT_ROOT>/src/index.js'
+module.file_ext=.js
+module.file_ext=.jsx
+module.file_ext=.json
+module.file_ext=.mjs
 module.file_ext=.tsx
 module.name_mapper.extension='tsx' -> 'any'
 module.name_mapper.extension='ts' -> 'any'

src/App.js

@@ -9,6 +9,7 @@ import React from 'react';
 import {FlexColumn, FlexRow} from 'flipper';
 import {connect} from 'react-redux';
 import WelcomeScreen from './chrome/WelcomeScreen.js';
+// $FlowFixMe T47375728
 import TitleBar from './chrome/TitleBar.tsx';
 import MainSidebar from './chrome/MainSidebar.js';
 import BugReporterDialog from './chrome/BugReporterDialog.js';

src/chrome/__tests__/TitleBar.electron.js

@@ -5,6 +5,7 @@
  * @format
  */
 
+// $FlowFixMe T47375728
 import TitleBar from '../TitleBar.tsx';
 import renderer from 'react-test-renderer';
 import reducers from '../../reducers/index.js';

src/utils/CertificateProvider.js

@@ -21,6 +21,7 @@ import iosUtil from '../fb-stubs/iOSContainerUtility';
 import {reportPlatformFailures} from './metrics';
 import {getAdbClient} from './adbClient';
 import * as androidUtil from './androidContainerUtility';
+// $FlowFixMe T47375728
 import dateFormat from 'dateformat';
 const writeFile = promisify(fs.writeFile);
 const exists = promisify(fs.exists);

src/utils/__tests__/Idler.node.js

@@ -17,6 +17,7 @@ test('Idler should interrupt', async () => {
       }
       await idler.idle();
     }
+    // $FlowFixMe T47375728
     fail('Idler should have thrown an error');
   } catch (e) {
     expect(i).toEqual(100);

src/utils/reduxDevToolsConfig.js

@@ -5,6 +5,7 @@
  * @format
  */
 
+// $FlowFixMe T47375728
 export const stateSanitizer = state => {
   let sanitizedState = state;
   if (state.connections) {