[Gradle, JS] Configure ir target in legacy plugin

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/KotlinJsTargetConfigurator.kt

@@ -59,7 +59,5 @@ open class KotlinJsTargetConfigurator(kotlinPluginVersion: String, val irConfigu
                 sourceMapEmbedSources = null
             }
         }
-
-        irConfigurator?.configureCompilations(target.irTarget!!)
     }
 }

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/KotlinJsTargetPreset.kt

@@ -56,7 +56,10 @@ open class KotlinJsTargetPreset(
             }
         }
 
-        createKotlinTargetConfigurator().configureTarget(result)
+        createKotlinTargetConfigurator().apply {
+            irConfigurator?.configureTarget(result.irTarget!!, true)
+            configureTarget(result)
+        }
 
         return result
     }
@@ -89,7 +92,8 @@ class KotlinJsSingleTargetPreset(
 ) {
 
     // In a Kotlin/JS single-platform project, we don't need any disambiguation suffixes or prefixes in the names:
-    override fun provideTargetDisambiguationClassifier(target: KotlinOnlyTarget<KotlinJsCompilation>): String? = null
+    override fun provideTargetDisambiguationClassifier(target: KotlinOnlyTarget<KotlinJsCompilation>): String? =
+        irPreset?.let { "legacy${target.name}" }
 
     override fun createKotlinTargetConfigurator() = KotlinJsTargetConfigurator(
         kotlinPluginVersion,

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/ir/KotlinJsIrTargetConfigurator.kt

@@ -21,6 +21,11 @@ open class KotlinJsIrTargetConfigurator(kotlinPluginVersion: String) :
 
     override val testRunClass: Class<KotlinJsIrReportAggregatingTestRun> get() = KotlinJsIrReportAggregatingTestRun::class.java
 
+    @Deprecated("Remove when legacy js plugin will be removed")
+    fun configureTarget(target: KotlinJsIrTarget, mixedMode: Boolean) {
+        super<KotlinOnlyTargetConfigurator>.configureTarget(target) // TODO Add tests support
+    }
+
     override fun createTestRun(
         name: String,
         target: KotlinJsIrTarget