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/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) {