JDK 14 RFR of JDK-8233096: Update javax.lang.model for switch expressions

[Joe Darcy]

Hello,

After switch expressions are added as a full non-preview feature 
(JDK-8232684), portions of javax.lang.model should be updated 
accordingly, including the description of SourceVersion.RELEASE_14.

Please review the changes for this:

     http://cr.openjdk.java.net/~darcy/8233096.0/

Thanks,

-Joe