Add JS stdlib dependency only when JS target is set

^KT-41642 In Progress

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

@@ -193,12 +193,21 @@ abstract class KotlinJsProjectExtension(project: Project) :
 
     lateinit var legacyPreset: KotlinJsSingleTargetPreset
 
+    private val targetSetObservers = mutableListOf<(KotlinJsTargetDsl?) -> Unit>()
+
     // target is public property
     // Users can write kotlin.target and it should work
     // So call of target should init default configuration
     @Deprecated("Use `target` instead", ReplaceWith("target"))
     var _target: KotlinJsTargetDsl? = null
-        private set
+        private set(value) {
+            field = value
+            targetSetObservers.forEach { it(value) }
+        }
+
+    internal fun registerTargetObserver(observer: (KotlinJsTargetDsl?) -> Unit) {
+        targetSetObservers.add(observer)
+    }
 
     companion object {
         internal fun reportJsCompilerMode(compilerType: KotlinJsCompilerType) {

libraries/tools/kotlin-gradle-plugin/src/common/kotlin/org/jetbrains/kotlin/gradle/internal/KotlinDependenciesManagement.kt

@@ -130,6 +130,9 @@ private fun Project.configureStdlibDefaultDependency(
 
     when {
         project.hasKpmModel -> addStdlibToKpmProject(project, coreLibrariesVersion)
+        topLevelExtension is KotlinJsProjectExtension -> topLevelExtension.registerTargetObserver { target ->
+            target?.addStdlibDependency(configurations, dependencies, coreLibrariesVersion)
+        }
         topLevelExtension is KotlinSingleTargetExtension<*> -> topLevelExtension
             .target
             .addStdlibDependency(configurations, dependencies, coreLibrariesVersion)
@@ -297,6 +300,16 @@ private fun Project.configureKotlinTestDependency(
     coreLibrariesVersion: Provider<String>,
 ) {
     when (topLevelExtension) {
+        is KotlinJsProjectExtension -> topLevelExtension.registerTargetObserver { target ->
+            target?.configureKotlinTestDependency(
+                configurations,
+                coreLibrariesVersion,
+                objects,
+                dependencies,
+                tasks
+            )
+        }
+
         is KotlinSingleTargetExtension<*> -> topLevelExtension.target.configureKotlinTestDependency(
             configurations,
             coreLibrariesVersion,