Issue #8832 makes a good point that we should not be making
implicit assumptions about the client's performance
when waiting for internal events. At the same time,
we want to be able to get the debug info if some promises
never resolve because of missing backend events.
This PR adds a variable to turn on timeouts for deferred
promises created using `createDebuggableDeferredPromise`.
We can use it in our tests to catch never-resolving
promises or when reproducing bug reports where Puppeteer
hangs indefinitely.
Closes#8832
