[Gradle, JS] Add toStringLoader for imported

#KT-38055 fixed

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

@@ -28,6 +28,7 @@ class NpmVersions {
 
     val cssLoader = NpmPackageVersion("css-loader", "3.4.2")
     val styleLoader = NpmPackageVersion("style-loader", "1.1.3")
+    val toStringLoader = NpmPackageVersion("to-string-loader", "1.1.6")
     val miniCssExtractPlugin = NpmPackageVersion("mini-css-extract-plugin", "0.9.0")
 
     val mocha = NpmPackageVersion("mocha", "7.1.1")

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

@@ -64,8 +64,7 @@ data class KotlinWebpackConfig(
                 when (rule.mode) {
                     EXTRACT -> it.add(versions.miniCssExtractPlugin)
                     INLINE -> it.add(versions.styleLoader)
-                    IMPORT -> {
-                    }
+                    IMPORT -> it.add(versions.toStringLoader)
                     else -> cssError()
                 }
             }
@@ -285,6 +284,15 @@ data class KotlinWebpackConfig(
             |       
             """.trimMargin()
 
+        val importedCss =
+            """
+            |       use.unshift({
+            |           loader: 'to-string-loader',
+            |           options: {}
+            |       })
+            |       
+            """.trimMargin()
+
         cssSettings.rules.forEach { rule ->
             appendln(
                 """
@@ -305,8 +313,7 @@ data class KotlinWebpackConfig(
             when (rule.mode) {
                 EXTRACT -> appendln(extractedCss)
                 INLINE -> appendln(inlinedCss)
-                IMPORT -> {
-                }
+                IMPORT -> appendln(importedCss)
                 else -> cssError()
             }