JDK 12 RFR of JDK-8173606: Deprecate constructors of 7-era visitors

[joe darcy]

Hello,

Please review the changeset

     JDK-8173606: Deprecate constructors of 7-era visitors
     http://cr.openjdk.java.net/~darcy/8173606.0/

and corresponding CSR

         https://bugs.openjdk.java.net/browse/JDK-8206878

The changeset follows the pattern previously established for deprecating 
the JDK 6-era visitors in the same release as -source/-target 6 was made 
obsolete.

Thanks,

-Joe