Fix GH-12837: Combination of phpdbg and Generator method causes memory leak

The fix for bug #72523 (d1dd474) added a check on `zend_execute_ex` to
add an extra refcount to `This`. This is necessary because the VM does a
re-entry here:

https://github.com/php/php-src/blob/ecb90c1db7efe9d87c07e31336185fc393281035/Zend/zend_vm_def.h#L4294-L4299

and then cleans up `This` here:

https://github.com/php/php-src/blob/ecb90c1db7efe9d87c07e31336185fc393281035/Zend/zend_vm_def.h#L4358-L4360

So if we don't add the refcount, we destroy `This` both in the VM and in
`zend_generator_close`.

The reason this causes a leak in phpdbg is because it changes the
`zend_execute_ex` temporarily back to the default here for `ZEND_DO_FCALL`:
https://github.com/php/php-src/blob/ecb90c1db7efe9d87c07e31336185fc393281035/sapi/phpdbg/phpdbg_prompt.c#L1820-L1827
which means that we only execute `OBJ_RELEASE` on the `This` object once
in `zend_generator_close` instead of also doing it in the
`ZEND_DO_FCALL` handler.

To solve this, we make sure the check for the re-entrancy is
consistently done by checking the `ZEND_CALL_TOP` flag instead of
relying solely on `execute_ex` pointer:

https://github.com/php/php-src/blob/ecb90c1db7efe9d87c07e31336185fc393281035/Zend/zend_vm_def.h#L4298

Author: nielsdos

Zend/zend_vm_def.h

@@ -4534,7 +4534,7 @@ ZEND_VM_HANDLER(139, ZEND_GENERATOR_CREATE, ANY, ANY)
 		if ((call_info & Z_TYPE_MASK) == IS_OBJECT
 		 && (!(call_info & (ZEND_CALL_CLOSURE|ZEND_CALL_RELEASE_THIS))
 			 /* Bug #72523 */
-			|| UNEXPECTED(zend_execute_ex != execute_ex))) {
+			|| (call_info & ZEND_CALL_TOP))) {
 			ZEND_ADD_CALL_FLAG_EX(call_info, ZEND_CALL_RELEASE_THIS);
 			Z_ADDREF(gen_execute_data->This);
 		}

Zend/zend_vm_execute.h

@@ -0,0 +1,44 @@
+--TEST--
+GH-12837 (Combination of phpdbg and Generator method causes memory leak)
+--CREDITS--
+ngyuki
+--FILE--
+<?php
+class A
+{
+    public function __construct()
+    {
+        var_dump('__construct');
+    }
+
+    public function __destruct()
+    {
+        var_dump('__destruct');
+    }
+
+    public function iterate()
+    {
+        yield 1;
+    }
+}
+
+$arr = iterator_to_array((new A())->iterate()); gc_collect_cycles();
+$arr = iterator_to_array((new A())->iterate()); gc_collect_cycles();
+$arr = iterator_to_array((new A())->iterate()); gc_collect_cycles();
+
+var_dump('exit');
+?>
+--PHPDBG--
+r
+q
+--EXPECTF--
+[Successful compilation of %s]
+prompt> string(11) "__construct"
+string(10) "__destruct"
+string(11) "__construct"
+string(10) "__destruct"
+string(11) "__construct"
+string(10) "__destruct"
+string(4) "exit"
+[Script ended normally]
+prompt>