[php-src] Issue #11389: Allow suspending fibers in destructors

Issue: https://github.com/php/php-src/issues/11389 Author: nicolas-grekas ### Description Right now, when trying to suspend the current fiber in a destructor, the engine throws "Cannot switch fibers in current execution context". This has been discussed a bit with @trowski and @kelunik in https://github.com/nicolas-grekas/symfony/pull/43#pullrequestreview-1426674302 From that discussion, the reason is that the garbage collector would need to be made safe for re-entry from multiple fibers. Not being able to do i/o (which is what fibers are most useful for) in destructors kinda reintroduces the “What color is your function?” problem, which fibers were designed to avoid. I totally get that this might be challenging, but this limitation should be removed if possible. :pray: