addresses https://github.com/protocolbuffers/protobuf/issues/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
Brent Shaffer