[vector] RFR: Don't dump IR for unused VectorBox nodes

[Paul Sandoz]

+1
Paul.

> On Apr 7, 2020, at 6:45 AM, Vladimir Ivanov <vladimir.x.ivanov at oracle.com> wrote:
> 
> http://cr.openjdk.java.net/~vlivanov/panama/vector/igv/webrev.00/
> 
> To simplify ideal graph analysis, don't dump IR for unused VectorBox nodes.
> 
> Testing: jdk/incubator/vector tests
> 
> The patch is against vectorIntrinsics branch.
> 
> Best regards,
> Vladimir Ivanov