[php-src] Issue #8078: `eval` is leaking memory

Issue: https://github.com/php/php-src/issues/8078 Comment Author: nikic It requires moving away from arena allocation. I believe it's not entirely simple because we have two different ways to share op_arrays, one of them sharing only the resources it points to while having a separately allocated op_array structure, and another where the op_array itself is also shared. This makes it a bit tricky to determine whether or not an op_array needs to be freed when it is released, or only the refcount decremented.