Generational ZGC: Clearing All SoftReferences log line lacks GCId

[3.589s][info][gc,ref ] Clearing All SoftReferences
[3.589s][info][gc ] GC(36) Major Collection (Allocation Stall)
[3.589s][info][gc,task ] GC(36) Using 1 Workers for Young Generation
[3.589s][info][gc,task ] GC(36) Using 1 Workers for Old Generation
[3.589s][info][gc,phases ] GC(36) Y: Young Generation (Promote All)

This happens because the logging happens outside the the gc scope:
```
    // Set up soft reference policy
    const bool clear_soft_refs = should_clear_soft_references(request.cause());
    ZGeneration::old()->set_soft_reference_policy(clear_soft_refs);

    // Run GC
    gc(request);
```