Keep image zone rules cache separate oracle#2637

* Before this patch,
the image would contain zone rules cache from the JVM computing the image.
* Side effects here,
such as class or source cache lookups,
were affecting its contents and leading to error when writing image.
* With this change,
we guarantee that the zone rules cache in the image is a brand new instance,
separate from the one in the JVM computing the image.

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/jdk/TimeSubstitutions.java

@@ -0,0 +1,23 @@
+package com.oracle.svm.core.jdk;
+
+import com.oracle.svm.core.annotate.Alias;
+import com.oracle.svm.core.annotate.RecomputeFieldValue;
+import com.oracle.svm.core.annotate.TargetClass;
+
+import java.time.zone.ZoneOffsetTransition;
+import java.time.zone.ZoneRules;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+
+@TargetClass(ZoneRules.class)
+final class Target_java_time_zone_ZoneRules {
+
+    @SuppressWarnings("unused")
+    @Alias
+    @RecomputeFieldValue(kind = RecomputeFieldValue.Kind.NewInstance, declClass = ConcurrentHashMap.class)
+    private transient ConcurrentMap<Integer, ZoneOffsetTransition[]> lastRulesCache;
+
+}
+
+class TimeSubstitutions {
+}