Use logger-neutral API

[desruisseaux]

PROJ-JNI uses java.util.logging for reporting warnings. But other logging frameworks such as SLF4J are popular. Since Java 9, a more framework-neutral API is available with System.Logger. We should replace our usage of java.util.logging by System.Logger.

A difficulty is that current PROJ-JNI is still targeting Java 8. We could use multi-versions JAR file for taking advantage of System.Logger automatically when the execution environment is Java 9 or later. However we are invoking java.util.logging from native code as well. The NativeResource.logger() method is invoked from JNI code. Trying to support multi-versions in JNI code would be too difficult and risky. Consequently, this issue is reminder for a task to do after #65 is resolved.