KT-56687: Unify handling of EnumEntries.

`supportsEnumEntries` in `EnumCLassLowering` is not really
needed, but it was left just in case.
Both K1 and K2 ensure the feature is
enabled before they generate IR.

`supportsEnumEntries` is not enough, because the frontend will not
generate `entries` if `kotlin.enums.EnumEntries` is not available
(linking against an outdated stdlib is considered a valid use-case).

From the resolution point of view,
it's OK to resolve into `entries` while
the feature is off, because then K1 reports an error on the call site.

^KT-56687 Fixed
^KT-55614 Fixed

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/EnumEntriesWithOutdatedStdlibTest.kt

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.gradle
+
+import org.gradle.util.GradleVersion
+import org.jetbrains.kotlin.gradle.testbase.*
+import org.jetbrains.kotlin.gradle.util.replaceText
+import org.junit.jupiter.api.DisplayName
+
+@DisplayName("EnumEntries feature test when no kotlin.enums.EnumEntries found on the classpath")
+@JvmGradlePluginTests
+class EnumEntriesWithOutdatedStdlibTest : KGPBaseTest() {
+    @DisplayName("EnumEntries should not be accessible without kotlin.enums.EnumEntries")
+    @GradleTest
+    fun enumEntriesNotAccessible(gradleVersion: GradleVersion) {
+        project("enumEntriesNotAccessible", gradleVersion) {
+            buildGradleKts.replaceText("\"<language-version>\"", "\"1.9\" // <language-version>")
+
+            buildAndFail(":compileKotlin") {
+                assertOutputContains("Main.kt:13:20 Unresolved reference: entries")
+                assertOutputContains("Main.kt:14:30 Unresolved reference: entries")
+            }
+
+            buildGradleKts.replaceText("\"1.9\" // <language-version>", "\"2.0\" // <language-version>")
+
+            buildAndFail(":compileKotlin") {
+                assertOutputContains("Main.kt:13:20 Unresolved reference: entries")
+                assertOutputContains("Main.kt:14:30 Unresolved reference: entries")
+            }
+        }
+    }
+
+    @DisplayName("Code should compile normally if `entries` is never referenced")
+    @GradleTest
+    fun codeCompilesWithoutReferencingEntries(gradleVersion: GradleVersion) {
+        project("enumEntriesNotAccessible", gradleVersion) {
+            projectPath.resolve("src/main/kotlin/Main.kt")
+                .replaceText("entries", "values()")
+
+            buildGradleKts.replaceText("\"<language-version>\"", "\"1.9\" // <language-version>")
+            build(":compileKotlin")
+
+            buildGradleKts.replaceText("\"1.9\" // <language-version>", "\"2.0\" // <language-version>")
+            build(":compileKotlin")
+        }
+    }
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/enumEntriesNotAccessible/build.gradle.kts

@@ -0,0 +1,24 @@
+import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
+
+plugins {
+    kotlin("jvm")
+}
+
+group = "com.example"
+version = "1.0"
+
+dependencies {
+    implementation("org.jetbrains.kotlin:kotlin-stdlib:1.7.20")
+}
+
+allprojects {
+    repositories {
+        mavenLocal()
+        mavenCentral()
+    }
+}
+
+tasks.withType<KotlinCompile> {
+    kotlinOptions.jvmTarget = "1.8"
+    kotlinOptions.languageVersion = "<language-version>"
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/enumEntriesNotAccessible/settings.gradle

@@ -0,0 +1,2 @@
+include(":k1")
+include(":k2")

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/enumEntriesNotAccessible/src/main/kotlin/Main.kt

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package com.example
+
+enum class MyEnum {
+    A, B
+}
+
+fun main() {
+    val a = MyEnum.entries
+    val b = AnnotationTarget.entries
+    println("$a :: $b")
+}