dillon1000/react

Convert class equivlance tests to flushSync (#26333)

There's an old collection of test suites that test class component
behavior across ES6 (regular JavaScript classes), CoffeeScript classes,
and TypeScript classes. They work by running the same tests in all
environments and comparing the results.

Rather than use `act` or `waitFor` in these, I've changed them to use
`flushSync` instead so that they can flush synchronously. The reason is
that CoffeeScript doesn't have async/await, so we'd have to write those
tests differently than how they are written in the corresponding
modules. Since none of these tests cover any concurrent behavior, I
believe it's fine in this case to do everything synchronously; they
don't use any concurrent features, anyway, so effectively it's just
skipping a microtask.