Change dsl method to 'jvmToolchain'.

This better reflects that applying toolchain only affects jvm
backend compilations.

^KT-43095 In Progress

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/KotlinJavaToolchainTest.kt

@@ -404,7 +404,7 @@ class KotlinJavaToolchainTest : KGPBaseTest() {
             import org.gradle.jvm.toolchain.JavaToolchainService
             
             kotlin {
-                toolchain {
+                jvmToolchain {
                     languageVersion.set(JavaLanguageVersion.of($jdkVersion))
                 }
             }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/dsl/KotlinProjectExtension.kt

@@ -64,11 +64,11 @@ open class KotlinTopLevelExtension (internal val project: Project) {
     private val toolchainSupport = ToolchainSupport.createToolchain(project)
 
     /**
-     * Configures [Java toolchain](https://docs.gradle.org/current/userguide/toolchains.html) both for Kotlin and Java tasks.
+     * Configures [Java toolchain](https://docs.gradle.org/current/userguide/toolchains.html) both for Kotlin JVM and Java tasks.
      *
      * @param action - action to configure [JavaToolchainSpec]. You could safely cast `Any` into `JavaToolchainSpec`.
      */
-    fun toolchain(action: Action<Any>) {
+    fun jvmToolchain(action: Action<Any>) {
         toolchainSupport.applyToolchain(action)
     }