Introduce KotlinJavaToolchain compile tasks input.

This task input provides a way to set different from current Gradle
JDK and use it for Kotlin files compilation. By default it provides
current Gradle JDK.

Provided JDK major version is used as task input, so on providing
different JDK user will see cache miss.

All required interfaces are located inside api module.

^KT-45611 In Progress

libraries/tools/kotlin-gradle-plugin-api/src/main/kotlin/org/jetbrains/kotlin/gradle/tasks/UsesKotlinJavaToolchain.kt

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.gradle.tasks
+
+import org.gradle.api.JavaVersion
+import org.gradle.api.provider.Provider
+import org.gradle.api.tasks.Input
+import org.gradle.api.tasks.Internal
+import org.gradle.api.tasks.Nested
+import java.io.File
+
+interface UsesKotlinJavaToolchain {
+    @get:Nested
+    val kotlinJavaToolchainProvider: Provider<out KotlinJavaToolchain>
+
+    @get:Internal
+    val kotlinJavaToolchain: KotlinJavaToolchain
+        get() = kotlinJavaToolchainProvider.get()
+}
+
+interface KotlinJavaToolchain {
+    @get:Input
+    val javaVersion: Provider<JavaVersion>
+
+    /**
+     * Set JDK to use for Kotlin compilation.
+     *
+     * Major JDK version is considered as compile task input.
+     *
+     * @param jdkHomeLocation path to JDK.
+     * *Note*: project build will fail on providing here JRE instead of JDK!
+     * @param jdkVersion provided JDK version
+     */
+    fun setJdkHome(
+        jdkHomeLocation: File,
+        jdkVersion: JavaVersion
+    )
+
+    /**
+     * Set JDK to use for Kotlin compilation.
+     *
+     * @see [setJdkHome]
+     */
+    fun setJdkHome(
+        jdkHomeLocation: String,
+        jdkVersion: JavaVersion
+    ) = setJdkHome(File(jdkHomeLocation), jdkVersion)
+}