Shenandoah: SBSC2::is_shenandoah_lrb_call should match all LRB shapes

In current code, we match only one LRB shape:

 bool ShenandoahBarrierSetC2::is_shenandoah_lrb_call(Node* call) {
   return call->is_CallLeaf() &&
           call->as_CallLeaf()->entry_point() == CAST_FROM_FN_PTR(address, ShenandoahRuntime::load_reference_barrier);
 }

...which is not the only shape that is emitted by C2 code.

Current bug is somewhat benign, because SBSC2::is_shenandoah_lrb_call is used in C2 verification code only, but it could be catastrophic in future.