Fix failure when creating a compilation in afterEvaluate (KT-28896)

To configure a compilation's sources, we run an action in
`whenEvaluated { ... }`, expecting that the compilation's task already
exists. This was not true with compilations created from a user build
script or a 3rd-party plugin in `afterEvaluate { ... }`.

Fix this by expecting that a task may possibly not exist at that point,
and also using `whenEvaluated { ... }` instead of
`afterEvaluate { ... }` in several places that are executed for each new
compilation as a workaround for
https://github.com/gradle/gradle/issues/1135.

Issue #KT-28896 Fixed

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/new-mpp-lib-and-app/sample-lib-gradle-kotlin-dsl/build.gradle.kts

@@ -54,3 +54,13 @@ publishing {
 		maven { setUrl("file://${projectDir.absolutePath.replace('\\', '/')}/repo") }
 	}
 }
+
+// Check that a compilation may be created after project evaluation, KT-28896:
+afterEvaluate {
+    kotlin {
+        jvm("jvm6").compilations.create("benchmark") {
+            defaultSourceSet.dependsOn(sourceSets["jvm6Main"])
+            tasks["assemble"].dependsOn(compileKotlinTask)
+        }
+    }
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/new-mpp-lib-and-app/sample-lib/build.gradle

@@ -84,3 +84,13 @@ publishing {
 		maven { url "file://${projectDir.absolutePath.replace('\\', '/')}/repo" }
 	}
 }
+
+// Check that a compilation may be created after project evaluation, KT-28896:
+afterEvaluate {
+    kotlin {
+        jvm('jvm6').compilations.create('benchmark') {
+            defaultSourceSet.dependsOn(sourceSets.jvm6Main)
+            assemble.dependsOn compileKotlinTask
+        }
+    }
+}

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/kotlinCompilations.kt

@@ -81,13 +81,22 @@ abstract class AbstractKotlinCompilation<T : KotlinCommonOptions>(
                 commonSourceSet += sourceSet.kotlin
             }
         }
-        // Note! Invocation of getByName results in preliminary task instantiation. After fix of this issue the following code should be uncommented:
+
+        // Note! Invocation of withType-all results in preliminary task instantiation.
+        // After fix of this issue the following code should be uncommented:
 //        if (useLazyTaskConfiguration) {
 //            (target.project.tasks.named(compileKotlinTaskName) as TaskProvider<AbstractKotlinCompile<*>>).configure {
 //                it.configureAction()
 //            }
 //        }
-        (target.project.tasks.getByName(compileKotlinTaskName) as AbstractKotlinCompile<*>).configureAction()
+
+        target.project.tasks
+            // To configure a task that may have not yet been created at this point, use 'withType-matching-all`:
+            .withType(AbstractKotlinCompile::class.java)
+            .matching { it.name == compileKotlinTaskName }
+            .all { compileKotlinTask ->
+                compileKotlinTask.configureAction()
+            }
     }
 
     override fun source(sourceSet: KotlinSourceSet) {