[java-dfa] PlainDescriptor: use identityHashCode

Improves LiveVariableAnalyzer performance, when there are many identically-named variables, as we have much less hash collisions
Improves IDEA-375149 Slow Java Debugger Data Views - ControlFlowAnalyzer.buildControlFlow()

GitOrigin-RevId: b9e7127cdfd2d4696f7066c3c48d5711cecab415

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/jvm/descriptors/PlainDescriptor.java

@@ -34,7 +34,7 @@ public final class PlainDescriptor extends PsiVarDescriptor {
 
   public PlainDescriptor(@NotNull PsiVariable variable) {
     myVariable = variable;
-    myHash = Objects.hashCode(variable.getName());
+    myHash = System.identityHashCode(variable);
   }
 
   @Override

java/java-tests/testSrc/com/intellij/java/codeInspection/DataFlowInspectionTest.java

@@ -762,4 +762,6 @@ public class DataFlowInspectionTest extends DataFlowInspectionTestCase {
   public void testIoContracts() { doTest(); }
   public void testGetTernary() { doTest(); }
   public void testClosureInConstructor() { doTest(); }
+  
+  public void testHugeMethodFlow() { doTest(); }
 }