Add a property to configure eager constants

In order to avoid polluting the Java:: namespace with classes from
other classloader hierarchies, we are modifying the proxy class
setup process to not eagerly set a constant for newly-encountered
classes. This property controls the behavior, defaulting to true
for JRuby 9.4.x but likely to switch to false in a future release
(probably JRuby 10).

The constants will still be defined if accessed directly, as
before. We just won't define them when we happen to see an object
with an unfamiliar type.

See jruby#8208 and the bug it fixed jruby#8156.

core/src/main/java/org/jruby/javasupport/Java.java

@@ -414,7 +414,7 @@ public static RubyModule getProxyClass(Ruby runtime, JavaClass javaClass) {
 
     @SuppressWarnings("deprecation")
     public static RubyModule getProxyClass(final Ruby runtime, final Class<?> clazz) {
-        return getProxyClass(runtime, clazz, false);
+        return getProxyClass(runtime, clazz, Options.JI_EAGER_CONSTANTS.load());
     }
 
     @SuppressWarnings("deprecation")

core/src/main/java/org/jruby/util/cli/Options.java

@@ -194,6 +194,7 @@ public class Options {
     public static final Option<Boolean> JI_LOAD_LAZY = bool(JAVA_INTEGRATION, "ji.load.lazy", true, "Load Java support (class extensions) lazily on demand or ahead of time.");
     public static final Option<Boolean> JI_CLOSE_CLASSLOADER = bool(JAVA_INTEGRATION, "ji.close.classloader", false, "Close the JRubyClassLoader used by each runtime");
     public static final Option<String> JI_NESTED_JAR_TMPDIR = string(JAVA_INTEGRATION, "ji.nested.jar.tmpdir", "Use specified dir as a base for unpacking nested jar files.");
+    public static final Option<Boolean> JI_EAGER_CONSTANTS = bool(JAVA_INTEGRATION, "ji.eager.constants", true, "Eagerly bind Java:: constants for newly-encountered classes");
 
     public static final Option<Integer> PROFILE_MAX_METHODS = integer(PROFILING, "profile.max.methods", 100000, "Maximum number of methods to consider for profiling.");