Fix KNPE in "introduce variable", add some name conflict introduce tests

So #KT-21530 Fixed

idea/src/org/jetbrains/kotlin/idea/refactoring/introduce/introduceVariable/KotlinIntroduceVariableHandler.kt

@@ -529,7 +529,7 @@ object KotlinIntroduceVariableHandler : RefactoringActionHandler {
             else {
                 expression.parent as KtElement
             }
-            var commonContainer = commonParent.getContainer()!!
+            var commonContainer = commonParent as? KtFile ?: commonParent.getContainer()!!
             if (commonContainer != container && container.isAncestor(commonContainer, true)) {
                 commonContainer = container
             }

idea/testData/refactoring/introduceProperty/kt21530.kt

@@ -0,0 +1,6 @@
+// EXTRACTION_TARGET: property with initializer
+
+fun test() = "123"
+
+val f = <selection>test()</selection> + "456"
+val x = test()

idea/testData/refactoring/introduceProperty/kt21530.kt.after

@@ -0,0 +1,8 @@
+// EXTRACTION_TARGET: property with initializer
+
+fun test() = "123"
+
+private val s = test()
+
+val f = s + "456"
+val x = s

idea/testData/refactoring/introduceVariable/kt21530_withConstructorParam.kt

@@ -0,0 +1,8 @@
+fun test() = "123"
+
+open class First(val s: String)
+object Second : First(<selection>test()</selection> + "456")
+
+fun foo(test: String) {
+    val x = test()
+}

idea/testData/refactoring/introduceVariable/kt21530_withConstructorParam.kt.after

@@ -0,0 +1,11 @@
+fun test() = "123"
+
+open class First(val s: String)
+
+val test1 = test()
+
+object Second : First(test1 + "456")
+
+fun foo(test: String) {
+    val x = test1
+}

idea/testData/refactoring/introduceVariable/kt21530_withGlobal.kt

@@ -0,0 +1,4 @@
+fun test() = "123"
+
+val f = <selection>test()</selection> + "456"
+val x = test()

idea/testData/refactoring/introduceVariable/kt21530_withGlobal.kt.after

@@ -0,0 +1,5 @@
+fun test() = "123"
+
+val test = test()
+val f = test + "456"
+val x = test

idea/testData/refactoring/introduceVariable/kt21530_withParam.kt

@@ -0,0 +1,7 @@
+fun test() = "123"
+
+val f = <selection>test()</selection> + "456"
+
+fun foo(test: String) {
+    val x = test()
+}

idea/testData/refactoring/introduceVariable/kt21530_withParam.kt.after

@@ -0,0 +1,8 @@
+fun test() = "123"
+
+val test1 = test()
+val f = test1 + "456"
+
+fun foo(test: String) {
+    val x = test1
+}

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

@@ -236,6 +236,24 @@ public class ExtractionTestGenerated extends AbstractExtractionTest {
             doIntroduceVariableTest(fileName);
         }
 
+        @TestMetadata("kt21530_withConstructorParam.kt")
+        public void testKt21530_withConstructorParam() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/refactoring/introduceVariable/kt21530_withConstructorParam.kt");
+            doIntroduceVariableTest(fileName);
+        }
+
+        @TestMetadata("kt21530_withGlobal.kt")
+        public void testKt21530_withGlobal() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/refactoring/introduceVariable/kt21530_withGlobal.kt");
+            doIntroduceVariableTest(fileName);
+        }
+
+        @TestMetadata("kt21530_withParam.kt")
+        public void testKt21530_withParam() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/refactoring/introduceVariable/kt21530_withParam.kt");
+            doIntroduceVariableTest(fileName);
+        }
+
         @TestMetadata("LoopRange.kt")
         public void testLoopRange() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/refactoring/introduceVariable/LoopRange.kt");
@@ -3173,6 +3191,12 @@ public class ExtractionTestGenerated extends AbstractExtractionTest {
             doIntroducePropertyTest(fileName);
         }
 
+        @TestMetadata("kt21530.kt")
+        public void testKt21530() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/refactoring/introduceProperty/kt21530.kt");
+            doIntroducePropertyTest(fileName);
+        }
+
         @TestMetadata("primaryConstructorParameterReference.kt")
         public void testPrimaryConstructorParameterReference() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/refactoring/introduceProperty/primaryConstructorParameterReference.kt");