KT-31762: Fix completion in enum entries constructors

- The issue was caused by incorrect parsing of enum entry because of `$` in the `KotlinCompletionContributor::DEFAULT_DUMMY_IDENTIFIER`
  - Incorrect parsing caused arguments next to completed one to be recognized as another enum entries
- Change `KotlinCompletionContributor::isInClassHeader` to accept classes without bodies, so identifier without `$` is used inside enum entries constructors
- ^KT-31762 Fixed

idea/idea-completion/src/org/jetbrains/kotlin/idea/completion/KotlinCompletionContributor.kt

@@ -170,9 +170,9 @@ class KotlinCompletionContributor : CompletionContributor() {
     private fun isInClassHeader(tokenBefore: PsiElement?): Boolean {
         val classOrObject = tokenBefore?.parents?.firstIsInstanceOrNull<KtClassOrObject>() ?: return false
         val name = classOrObject.nameIdentifier ?: return false
-        val body = classOrObject.getBody() ?: return false
+        val headerEnd = classOrObject.body?.startOffset ?: classOrObject.endOffset
         val offset = tokenBefore.startOffset
-        return name.endOffset <= offset && offset <= body.startOffset
+        return name.endOffset <= offset && offset <= headerEnd
     }
 
     private fun specialLambdaSignatureDummyIdentifier(tokenBefore: PsiElement?): String? {

idea/idea-completion/testData/basic/common/KT31762.kt

@@ -0,0 +1,6 @@
+enum class A { AAA }
+enum class E(val one: A, val two: A) {
+    EE(A.<caret>, A.AAA)
+}
+
+// EXIST: AAA

idea/idea-completion/tests/org/jetbrains/kotlin/idea/completion/test/JSBasicCompletionTestGenerated.java

@@ -440,6 +440,11 @@ public class JSBasicCompletionTestGenerated extends AbstractJSBasicCompletionTes
             runTest("idea/idea-completion/testData/basic/common/KT13780_1.kt");
         }
 
+        @TestMetadata("KT31762.kt")
+        public void testKT31762() throws Exception {
+            runTest("idea/idea-completion/testData/basic/common/KT31762.kt");
+        }
+
         @TestMetadata("KT33903_1.kt")
         public void testKT33903_1() throws Exception {
             runTest("idea/idea-completion/testData/basic/common/KT33903_1.kt");

idea/idea-completion/tests/org/jetbrains/kotlin/idea/completion/test/JvmBasicCompletionTestGenerated.java

@@ -440,6 +440,11 @@ public class JvmBasicCompletionTestGenerated extends AbstractJvmBasicCompletionT
             runTest("idea/idea-completion/testData/basic/common/KT13780_1.kt");
         }
 
+        @TestMetadata("KT31762.kt")
+        public void testKT31762() throws Exception {
+            runTest("idea/idea-completion/testData/basic/common/KT31762.kt");
+        }
+
         @TestMetadata("KT33903_1.kt")
         public void testKT33903_1() throws Exception {
             runTest("idea/idea-completion/testData/basic/common/KT33903_1.kt");