fix(subscribe): ignore syncError when deprecated

[cartant]

Description:

This PR adds a failing test and fixes the problem with the implementation of subscribe that sees the catchError operator bypassed in some circumstances.

This will fix the behaviour when useDeprecatedSynchronousErrorHandling is false - i.e. the default version 6 behaviour.

Elsewhere, the syncErrorThrowable flag has no meaning unless useDeprecatedSynchronousErrorHandling is true.

So, when useDeprecatedSynchronousErrorHandling is false, it makes no sense to consider syncErrorThrowable when deciding between a call to _subscribe or _trySubscribe.

Whether or not - as discussed in the related issue - a getter should be added to InnerSubscriber to attempt to fix the deprecated behaviour is another (more complicated) matter. And one that need not be relevant to this PR. As noted in this comment, even with the getter added, the deprecated behaviour is still broken.

Related issue (if exists): #3740

[coveralls]

Coverage decreased (-0.2%) to 96.654% when pulling 44e1a27 on cartant:issue-3470 into d7bfc9d on ReactiveX:master.