Migrate repo to use JVM toolchains Gradle feature.

^KT-46972 Fixed

core/util.runtime/build.gradle.kts

@@ -3,8 +3,7 @@ plugins {
     id("jps-compatible")
 }
 
-jvmTarget = "1.6"
-javaHome = rootProject.extra["JDK_16"] as String
+project.configureJvmToolchain(JdkMajorVersion.JDK_1_6)
 
 dependencies {
     compileOnly(kotlinStdlib())
@@ -15,11 +14,6 @@ sourceSets {
     "test" {}
 }
 
-tasks.withType<JavaCompile> {
-    sourceCompatibility = "1.6"
-    targetCompatibility = "1.6"
-}
-
 tasks.withType<org.jetbrains.kotlin.gradle.tasks.KotlinCompile>().configureEach {
     kotlinOptions {
         freeCompilerArgs += "-Xsuppress-deprecated-jvm-target-warning"