feat: better debug info for PHP messages and repeated fields (#12718)

addresses #12714 by dumping more concise debug info for protobuf messages and repeated fields via the `serializeToJsonString` function. Additionally, message types which serialize into something other than an array (e.g. `Google\Protobuf\Value`, `Google\Protobuf\Timestamp`, etc) are handled in a special way to make their output consistent with other messages.

```php
$m = new Google\Protobuf\DoubleValue();
$m->setValue(1.5);
var_dump($m);
```
will output
```
object(Google\Protobuf\DoubleValue)#12 (1) {
  ["value"]=>
  float(1.5)
}
```

Closes #12718

COPYBARA_INTEGRATE_REVIEW=#12718 from bshaffer:php-add-debuginfo c40a6f9
PiperOrigin-RevId: 574115431

php/src/Google/Protobuf/Internal/Message.php

@@ -2014,4 +2014,56 @@ public function jsonByteSize()
         }
         return $size;
     }
+
+    public function __debugInfo()
+    {
+        if (is_a($this, 'Google\Protobuf\FieldMask')) {
+            return ['paths' => $this->getPaths()->__debugInfo()];
+        }
+
+        if (is_a($this, 'Google\Protobuf\Value')) {
+            switch ($this->getKind()) {
+                case 'null_value':
+                    return ['nullValue' => $this->getNullValue()];
+                case 'number_value':
+                    return ['numberValue' => $this->getNumberValue()];
+                case 'string_value':
+                    return ['stringValue' => $this->getStringValue()];
+                case 'bool_value':
+                    return ['boolValue' => $this->getBoolValue()];
+                case 'struct_value':
+                    return ['structValue' => $this->getStructValue()->__debugInfo()];
+                case 'list_value':
+                    return ['listValue' => $this->getListValue()->__debugInfo()];
+            }
+            return [];
+        }
+
+        if (is_a($this, 'Google\Protobuf\BoolValue')
+            || is_a($this, 'Google\Protobuf\BytesValue')
+            || is_a($this, 'Google\Protobuf\DoubleValue')
+            || is_a($this, 'Google\Protobuf\FloatValue')
+            || is_a($this, 'Google\Protobuf\StringValue')
+            || is_a($this, 'Google\Protobuf\Int32Value')
+            || is_a($this, 'Google\Protobuf\Int64Value')
+            || is_a($this, 'Google\Protobuf\UInt32Value')
+            || is_a($this, 'Google\Protobuf\UInt64Value')
+        ) {
+            return [
+                'value' => json_decode($this->serializeToJsonString(), true),
+            ];
+        }
+
+        if (
+            is_a($this, 'Google\Protobuf\Duration')
+            || is_a($this, 'Google\Protobuf\Timestamp')
+        ) {
+            return [
+                'seconds' => $this->getSeconds(),
+                'nanos' => $this->getNanos(),
+            ];
+        }
+
+        return json_decode($this->serializeToJsonString(), true);
+    }
 }

php/src/Google/Protobuf/Internal/RepeatedField.php

@@ -238,4 +238,17 @@ public function count(): int
     {
         return count($this->container);
     }
+
+    public function __debugInfo()
+    {
+        return array_map(
+            function ($item) {
+                if ($item instanceof Message || $item instanceof RepeatedField) {
+                    return $item->__debugInfo();
+                }
+                return $item;
+            },
+            iterator_to_array($this)
+        );
+    }
 }