fix($rootScope): reset internal phase on digest exception

[lgalfaso]

Cleanup the internal phase when there is a non-handled exception.

Closes: #13127

[gkalpak]

I am not sure this is the right thing to do. There are already several try-catch blocks inside $digest.

AFAICT, the issue with phase not being cleared up only happens in tests (when using the mocked $exceptionHandler). The exception that causes this is already caught inside the $digest() and passed to the $exceptionHandler. Normally, the $exceptionHandler just logs the error and goes on.
The mocked handler used in tests (as part of ngMock) rethrows the error and that is why the phase doesn't get cleared.
Maybe, we could solve it more elegantly by taking care of it inside the mocked $exceptionHandler.

Still, this would not solve the issue in case someone overwrites the $exceptionHandler to actually throw errors, but anyone doing so would be asking for it anyway 😛

I'm not saying this is wrong or that I know of a better way (have only looked into it superficially) - just raising some concern :)

BTW, is there any perf-hit by the extra try-catch block ? This path is super-hot, isn't it ?

[lgalfaso]

The more I think about this, then the more I think @gkalpak is right. The proper solution would need to come from angular-mock and $exceptionHandler