[gradle-plugin] Support headerFile property for dynamic libraries

tools/kotlin-native-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/tasks/KonanCompileTask.kt

@@ -21,6 +21,7 @@ import org.gradle.api.tasks.*
 import org.jetbrains.kotlin.gradle.plugin.*
 import org.jetbrains.kotlin.konan.target.CompilerOutputKind
 import org.jetbrains.kotlin.konan.util.visibleName
+import java.io.File
 
 enum class Produce(val cliOption: String, val kind: CompilerOutputKind) {
     PROGRAM("program", CompilerOutputKind.PROGRAM),
@@ -179,6 +180,9 @@ open class KonanCompileProgramTask: KonanCompileTask() {
 
 open class KonanCompileDynamicTask: KonanCompileTask() {
     override val produce: Produce  get() = Produce.DYNAMIC
+
+    val headerFile: File
+        @OutputFile get() = destinationDir.resolve("$artifactPrefix${artifactName}_api.h")
 }
 
 open class KonanCompileFrameworkTask: KonanCompileTask() {

tools/kotlin-native-gradle-plugin/src/test/groovy/org/jetbrains/kotlin/gradle/plugin/test/PathSpecification.groovy

@@ -38,6 +38,9 @@ class PathSpecification extends BaseKonanSpecification {
                                 if (!target.artifact.exists()) throw new Exception("Artifact doesn't exist. Type: \${artifact.name}, target: \${target.target}")
                             }
                         }
+                        for (target in konanArtifacts.dynamic) {
+                            if (!target.headerFile.exists()) throw new Exception("Header file doesn't exist. Target: \${target.target}")
+                        }
                     }
                 }
             """.stripIndent())