JDK 13 RFR of CSR JDK-8214829: Update preview language features for start of JDK 13

[joe darcy]

Hello,

Getting ready for JDK 13, please review the CSR for

     JDK-8214829: Update preview language features for start of JDK 13
     https://bugs.openjdk.java.net/browse/JDK-8214829

In brief, preview features, such as raw string literals and switch 
expressions in 12, are tied to a particular release value.

The CSR proposes to continue to allow these features to be used at the 
start of JDK 13 as now in JDK 12. This is not preclude a different 
stance toward those features (remove, keep as preview, graduate to 
normal feature) later in JDK 13.

Thanks,

-Joe