chore: upgrade to jest 24 (#15778)

* chore: upgrade to jest 24

* download react-is from npm manually

packages/react-devtools-shared/src/__tests__/utils.js

@@ -25,7 +25,7 @@ export function act(callback: Function): void {
   });
 
   // Flush Bridge operations
-  while (global.mockGetTimersCount() > 0) {
+  while (jest.getTimerCount() > 0) {
     actDOM(() => {
       actTestRenderer(() => {
         jest.runAllTimers();
@@ -49,8 +49,7 @@ export async function actAsync(
   });
 
   if (recursivelyFlush) {
-    // TODO (Jest v24)  Replace with jest.getTimerCount() after we upgrade Jest
-    while (global.mockGetTimersCount() > 0) {
+    while (jest.getTimerCount() > 0) {
       // $FlowFixMe Flow doens't know about "await act()" yet
       await actDOM(async () => {
         await actTestRenderer(async () => {