Add a test with various wait/act use cases (#7728)

### Summary & Motivation

For use as a reference and playground for testing act/waitFor behavior with and without our provider components.

### How I Tested These Changes

`yarn jest waitFor`

js_modules/dagit/packages/core/src/workspace/waitFor.test.tsx

@@ -0,0 +1,69 @@
+import {act, render, screen, waitFor} from '@testing-library/react';
+import * as React from 'react';
+
+import {TestProvider} from '../testing/TestProvider';
+
+describe('waitFor', () => {
+  describe('With TestProvider', () => {
+    const Test = () => (
+      <TestProvider>
+        <div>Hello</div>
+      </TestProvider>
+    );
+
+    it('does require `act` if not wrapped in `waitFor`', async () => {
+      await act(async () => {
+        render(<Test />);
+      });
+      expect(screen.getByText(/hello/i)).toBeVisible();
+    });
+
+    it('does not require `act` if wrapped in `waitFor`', async () => {
+      render(<Test />);
+
+      await waitFor(() => {
+        expect(screen.getByText(/hello/i)).toBeVisible();
+      });
+    });
+  });
+
+  describe('Without TestProvider', () => {
+    it('does not require `act` if your rendered stuff is already there', () => {
+      const Test = () => <div>Hello</div>;
+      render(<Test />);
+      expect(screen.getByText(/hello/i)).toBeVisible();
+    });
+
+    describe('Rendering requires driving forward', () => {
+      const Test = () => {
+        const [value, setValue] = React.useState(0);
+        React.useEffect(() => {
+          const timer = setTimeout(() => {
+            setValue((current) => current + 1);
+          }, 0);
+          return () => {
+            clearTimeout(timer);
+          };
+        }, []);
+        return <div>Hello {value}</div>;
+      };
+
+      it('does require `act` if you need to drive rendering forward', async () => {
+        const {rerender} = render(<Test />);
+        expect(screen.getByText(/hello 0/i)).toBeVisible();
+
+        await act(async () => rerender(<Test />));
+        expect(screen.getByText(/hello 1/i)).toBeVisible();
+      });
+
+      it('or it requires a `wait` utility call if you need to drive rendering forward', async () => {
+        render(<Test />);
+        expect(screen.getByText(/hello 0/i)).toBeVisible();
+
+        await waitFor(() => {
+          expect(screen.getByText(/hello 1/i)).toBeVisible();
+        });
+      });
+    });
+  });
+});