JDK 15 RFR: JDK-8225361 : Start of release updates for JDK 15, includes JDK-8235497 and JDK-8235528

[Joe Darcy]

Hello,

The time approaches to being JDK 15! Please review the general langtools 
API and spec updates for this:

     http://cr.openjdk.java.net/~darcy/8225361.5/

The langtools portion includes two bugs with corresponding CSRs that 
also need review:

     JDK-8235497: Add SourceVersion.RELEASE_15
     CSR: https://bugs.openjdk.java.net/browse/JDK-8235498

     JDK-8235528: Add source 15 and target 15 to javac
     CSR: https://bugs.openjdk.java.net/browse/JDK-8235529

It might be time to retire the notion of profiles for new releases, but 
that can be decided another day.

Thanks,

-Joe