KT-7716 Introduce Variable's name suggestions often have "1" at the end for no real reason

#KT-7716 Fixed

idea/src/org/jetbrains/kotlin/idea/refactoring/NameValidatorImpl.kt

@@ -26,6 +26,7 @@ import org.jetbrains.kotlin.psi.JetExpression
 import org.jetbrains.kotlin.psi.JetVisitorVoid
 import org.jetbrains.kotlin.psi.psiUtil.siblings
 import org.jetbrains.kotlin.resolve.BindingContext
+import org.jetbrains.kotlin.resolve.descriptorUtil.isExtension
 import org.jetbrains.kotlin.resolve.lazy.BodyResolveMode
 import org.jetbrains.kotlin.resolve.scopes.JetScope
 
@@ -78,9 +79,9 @@ public class NameValidatorImpl(
                 if (!visitedScopes.add(resolutionScope)) return
 
                 val conflict =  if (target === Target.PROPERTIES)
-                    resolutionScope.getProperties(name).isNotEmpty() || resolutionScope.getLocalVariable(name) != null
+                    resolutionScope.getProperties(name).any { !it.isExtension } || resolutionScope.getLocalVariable(name) != null
                 else
-                    resolutionScope.getFunctions(name).isNotEmpty() || resolutionScope.getClassifier(name) != null
+                    resolutionScope.getFunctions(name).any { !it.isExtension } || resolutionScope.getClassifier(name) != null
 
                 if (conflict) {
                     conflictFound = true

idea/testData/refactoring/introduceVariable/NameSuggestionBug.kt

@@ -0,0 +1,8 @@
+class For
+
+val For.parent: For
+    get() = For()
+
+fun foo(f: For) {
+    <selection>f.parent</selection>
+}

idea/testData/refactoring/introduceVariable/NameSuggestionBug.kt.after

@@ -0,0 +1,8 @@
+class For
+
+val For.parent: For
+    get() = For()
+
+fun foo(f: For) {
+    val parent = f.parent
+}

idea/tests/org/jetbrains/kotlin/idea/refactoring/introduce/JetExtractionTestGenerated.java

@@ -163,6 +163,12 @@ public class JetExtractionTestGenerated extends AbstractJetExtractionTest {
             doIntroduceVariableTest(fileName);
         }
 
+        @TestMetadata("NameSuggestionBug.kt")
+        public void testNameSuggestionBug() throws Exception {
+            String fileName = JetTestUtils.navigationMetadata("idea/testData/refactoring/introduceVariable/NameSuggestionBug.kt");
+            doIntroduceVariableTest(fileName);
+        }
+
         @TestMetadata("noConflictWithInnerVariable.kt")
         public void testNoConflictWithInnerVariable() throws Exception {
             String fileName = JetTestUtils.navigationMetadata("idea/testData/refactoring/introduceVariable/noConflictWithInnerVariable.kt");