Make language settings nullable in KotlinModuleFragment

There is no lang settings when importing from klibs (yet)

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/mpp/GradleProjectModuleBuilder.kt

@@ -33,11 +33,11 @@ class ProjectStructureMetadataModuleBuilder {
     ): KotlinModule {
         val moduleData = BasicKotlinModule(component.toSingleModuleIdentifier()).apply {
             metadata.sourceSetNamesByVariantName.keys.forEach { variantName ->
-                fragments.add(BasicKotlinModuleVariant(this@apply, variantName, DefaultLanguageSettingsBuilder()))
+                fragments.add(BasicKotlinModuleVariant(this@apply, variantName))
             }
             fun fragment(sourceSetName: String): BasicKotlinModuleFragment {
                 if (fragments.none { it.fragmentName == sourceSetName })
-                    fragments.add(BasicKotlinModuleFragment(this@apply, sourceSetName, DefaultLanguageSettingsBuilder()))
+                    fragments.add(BasicKotlinModuleFragment(this@apply, sourceSetName))
                 return fragmentByName(sourceSetName)
             }
             metadata.sourceSetNamesByVariantName.forEach { (variantName, sourceSets) ->

libraries/tools/kotlin-project-model/src/main/kotlin/KotlinModuleFragment.kt

@@ -14,7 +14,7 @@ interface KotlinModuleFragment {
     val fragmentName: String
     val directRefinesDependencies: Iterable<KotlinModuleFragment>
 
-    val languageSettings: LanguageSettings
+    val languageSettings: LanguageSettings?
 
     // TODO: scopes
     val declaredModuleDependencies: Iterable<KotlinModuleDependency>
@@ -49,7 +49,7 @@ val KotlinModuleFragment.refinesClosure: Set<KotlinModuleFragment>
 open class BasicKotlinModuleFragment(
     override val containingModule: KotlinModule,
     override val fragmentName: String,
-    override val languageSettings: LanguageSettings
+    override val languageSettings: LanguageSettings? = null
 ) : KotlinModuleFragment {
 
     override val directRefinesDependencies: MutableSet<BasicKotlinModuleFragment> = mutableSetOf()
@@ -63,7 +63,7 @@ open class BasicKotlinModuleFragment(
 class BasicKotlinModuleVariant(
     containingModule: KotlinModule,
     fragmentName: String,
-    languageSettings: LanguageSettings
+    languageSettings: LanguageSettings? = null
 ) : BasicKotlinModuleFragment (
     containingModule,
     fragmentName,