This also changes timeout error format to
"page.click: Timeout 5000ms exceeded", so that all errors
can be similarly prefixed with api name.
We can now have different api names in different clients,
and our protocol is more reasonable.
A progress roughly corresponds to an api call. It is used:
- to collect logs related to the call;
- to handle timeout;
- to provide "cancellation token" behavior so that cancelable process can either
early-exit with progress.throwIfCanceled() or race against it with progress.race();
- to ensure resources are disposed in the case of a failure
with progress.cleanupWhenCanceled();
- (possibly) to log api calls if needed;
- (in the future) to augment async stacks.
