[Commonizer] Implement :native:kotlin-klib-commonizer:api with support for library commonization

- Implement new Gradle module ':native:kotlin-klib-commonizer'
- Implement new NativeKlibCommonize task
- Implement CommonizerTarget.identityString

native/commonizer-api/build.gradle.kts

@@ -0,0 +1,44 @@
+import org.jetbrains.kotlin.gradle.utils.NativeCompilerDownloader
+
+plugins {
+    kotlin("jvm")
+    id("jps-compatible")
+}
+
+kotlin {
+    explicitApi()
+}
+
+description = "Kotlin KLIB Library Commonizer API"
+publish()
+
+dependencies {
+    implementation(kotlinStdlib())
+    implementation(project(":native:kotlin-native-utils"))
+    testImplementation(project(":kotlin-test::kotlin-test-junit"))
+    testImplementation(commonDep("junit:junit"))
+    testImplementation(projectTests(":compiler:tests-common"))
+    testRuntimeOnly(project(":native:kotlin-klib-commonizer"))
+}
+
+sourceSets {
+    "main" { projectDefault() }
+    "test" { projectDefault() }
+}
+
+tasks.register("downloadNativeCompiler") {
+    doFirst {
+        NativeCompilerDownloader(project).downloadIfNeeded()
+    }
+}
+
+projectTest(parallel = false) {
+    dependsOn(":dist")
+    dependsOn("downloadNativeCompiler")
+    workingDir = projectDir
+    environment("KONAN_HOME", NativeCompilerDownloader(project).compilerDirectory.absolutePath)
+}
+
+runtimeJar()
+sourcesJar()
+javadocJar()