Heads up: J2ObjC build moving to JDK 11

[Tom Ball]

Currently, the J2ObjC project build depends on JDK 8 for Java compilation, and JDK 11 to build its Java module. As we upgrade to Android 13 (J2ObjC's JRE emulation library is a fork of Android's libcore library), we've seen some sources using language features from Java 9. These can't be built with JDK 8. Java releases frequently now, but long-term support (LTS) releases happen less often. Since the next LTS release after JDK 8 is JDK 11, we're changing the minimum version to JDK 11.

Please note this doesn't affect j2objc translation or Objective-C generation, just what JDK version is necessary to build J2ObjC from source.