Reset elementFinders on clearPackageCaches()

Clean up references on a plugin unload to avoid class leakage

Relates to #KT-49475

Merge-request: KT-MR-4891

compiler/resolution.common.jvm/src/org/jetbrains/kotlin/resolve/jvm/KotlinJavaPsiFacade.java

@@ -151,6 +151,7 @@ public class KotlinJavaPsiFacade implements Disposable {
     }
 
     private void clearPackageCaches(boolean force) {
+        elementFinders = null;
         if (force) {
             packageCache = null;
         } else {