feat(cdk/dialog): Support for Leaving Animation - wait for all child animations to complete before disposing the overlay [REOPEN]

[Sefibrah]

Feature Description

I am literally just reopening this already covered issue #28878

This time however, the @angular/cdk/dialog's leave animation doesn't work well even though the @angular/animations is deprecated.

There's not enough guidance on this. Is this our fault? Because it seems that the enter animation works fine.

[crisbeto]

There's no (performant) way of knowing if there are any pending animations inside the dialog so we can't really handle it on our end. We also likely wouldn't want to do it on our end, because it makes the closing of the dialog a bit unpredictable.

That being said, a couple of major versions ago we removed our dependency on @angular/animations which had the behavior of blocking child animations while the parent is animating which might affect your use case.