RFR (L): 8134994: use separate VMStructs databases for SA and JVMCI

[Christian Thalinger]

https://bugs.openjdk.java.net/browse/JDK-8134994 <https://bugs.openjdk.java.net/browse/JDK-8134994>
http://cr.openjdk.java.net/~twisti/8134994/webrev/ <http://cr.openjdk.java.net/~twisti/8134994/webrev/>

Currently JVMCI uses the existing VMStructs database which the SA also uses.  In order to be more flexible with the future of the SA the JVMCI should use it's own database.