PY-23623 Fixed: False positive: __getitem__ not being defined for list after isinstance check

While calculating severity, we infer type for qualifier in `v[0]` subscription expression.
While inferring type for qualifier, we infer type for `test_if_list` function.
While inferring type for `test_if_list` function, we infer `Any` type for `v` in `v[0]` to prevent recursion and resolve `[]` to nothing.
Unresolved `[]` is cached so when we ask for `[]` on `v[0]`, we receive nothing but at this moment we know type of `v` (`List[Any]`).

python/src/com/jetbrains/python/inspections/unresolvedReference/PyUnresolvedReferencesInspection.java

@@ -356,12 +356,7 @@ public class PyUnresolvedReferencesInspection extends PyInspection {
       if (!isEnabled(node) || reference == null || reference.isSoft()) {
         return;
       }
-      HighlightSeverity severity = HighlightSeverity.ERROR;
-      if (reference instanceof PsiReferenceEx) {
-        severity = ((PsiReferenceEx)reference).getUnresolvedHighlightSeverity(myTypeEvalContext);
-        if (severity == null) return;
-      }
-      PyExceptPart guard = getImportErrorGuard(node);
+      final PyExceptPart guard = getImportErrorGuard(node);
       if (guard != null) {
         processReferenceInImportGuard(node, guard);
         return;
@@ -375,7 +370,7 @@ public class PyUnresolvedReferencesInspection extends PyInspection {
         }
       }
       PsiElement target = null;
-      boolean unresolved;
+      final boolean unresolved;
       if (reference instanceof PsiPolyVariantReference) {
         final PsiPolyVariantReference poly = (PsiPolyVariantReference)reference;
         final ResolveResult[] resolveResults = poly.multiResolve(false);
@@ -405,6 +400,10 @@ public class PyUnresolvedReferencesInspection extends PyInspection {
           }
         }
         if (!ignoreUnresolved) {
+          final HighlightSeverity severity = reference instanceof PsiReferenceEx
+                                             ? ((PsiReferenceEx)reference).getUnresolvedHighlightSeverity(myTypeEvalContext)
+                                             : HighlightSeverity.ERROR;
+          if (severity == null) return;
           registerUnresolvedReferenceProblem(node, reference, severity);
         }
         // don't highlight unresolved imports as unused

python/testData/inspections/PyUnresolvedReferencesInspection/cachedOperatorInRecursivelyTypeInference.py

@@ -0,0 +1,9 @@
+def test_if_list(value):
+    if isinstance(value, list):
+        v = [test_if_list(x) for x in value]
+        if len(v) > 1:
+            return v
+        else:
+            return v[0]
+
+    return value

python/testSrc/com/jetbrains/python/inspections/PyUnresolvedReferencesInspectionTest.java

@@ -603,6 +603,11 @@ public class PyUnresolvedReferencesInspectionTest extends PyInspectionTestCase {
     doTest();
   }
 
+  // PY-23623
+  public void testCachedOperatorInRecursivelyTypeInference() {
+    doTest();
+  }
+
   @NotNull
   @Override
   protected Class<? extends PyInspection> getInspectionClass() {