MPP: Do not show -Xmultiplatform flag in facet settings

#KT-26484 Fixed

idea/idea-gradle/tests/org/jetbrains/kotlin/gradle/NewMultiplatformProjectImportingTest.kt

@@ -121,6 +121,10 @@ class NewMultiplatformProjectImportingTest : GradleImportingTestCase() {
             allModules {
                 languageVersion("1.2")
                 apiVersion("1.2")
+                when (module.name) {
+                    "project", "app", "lib" -> additionalArguments(null)
+                    else -> additionalArguments("-version")
+                }
             }
 
             module("project")

idea/idea-gradle/tests/org/jetbrains/kotlin/gradle/projectStructureDSL.kt

@@ -13,6 +13,7 @@ import com.intellij.openapi.roots.*
 import com.intellij.openapi.util.io.FileUtil
 import org.jetbrains.jps.model.module.JpsModuleSourceRootType
 import org.jetbrains.jps.util.JpsPathUtil
+import org.jetbrains.kotlin.idea.facet.KotlinFacet
 import org.jetbrains.kotlin.idea.project.languageVersionSettings
 import org.jetbrains.kotlin.idea.project.platform
 import org.jetbrains.kotlin.platform.IdePlatform
@@ -69,7 +70,7 @@ class ProjectInfo(project: Project, private val projectPath: String) {
 }
 
 class ModuleInfo(
-    private val module: Module,
+    val module: Module,
     private val messageCollector: MessageCollector,
     private val projectPath: String
 ) {
@@ -109,6 +110,15 @@ class ModuleInfo(
         }
     }
 
+    fun additionalArguments(arguments: String?) {
+        val actualArguments = KotlinFacet.get(module)?.configuration?.settings?.compilerSettings?.additionalArguments
+        if (actualArguments != arguments) {
+            messageCollector.report(
+                "Module '${module.name}': expected additional arguments '$arguments' but found '$actualArguments'"
+            )
+        }
+    }
+
     fun libraryDependency(libraryName: String, scope: DependencyScope) {
         val libraryEntry = rootModel.orderEntries.filterIsInstance<LibraryOrderEntry>().singleOrNull { it.libraryName == libraryName }
         if (libraryEntry == null) {

idea/idea-maven/test/org/jetbrains/kotlin/idea/maven/KotlinMavenImporterTest.kt

@@ -634,7 +634,7 @@ class KotlinMavenImporterTest : MavenImportingTestCase() {
             Assert.assertEquals("1.8", (compilerArguments as K2JVMCompilerArguments).jvmTarget)
             Assert.assertEquals("foobar.jar", (compilerArguments as K2JVMCompilerArguments).classpath)
             Assert.assertEquals(
-                "-Xmulti-platform",
+                "-version",
                 compilerSettings!!.additionalArguments
             )
         }
@@ -832,7 +832,7 @@ class KotlinMavenImporterTest : MavenImportingTestCase() {
                 Assert.assertEquals("commonjs", moduleKind)
             }
             Assert.assertEquals(
-                "-meta-info -output test.js -Xmulti-platform",
+                "-meta-info -output test.js",
                 compilerSettings!!.additionalArguments
             )
         }
@@ -984,7 +984,7 @@ class KotlinMavenImporterTest : MavenImportingTestCase() {
             Assert.assertEquals("JVM 1.8", platform!!.description)
             Assert.assertEquals("1.8", (compilerArguments as K2JVMCompilerArguments).jvmTarget)
             Assert.assertEquals("foobar.jar", (compilerArguments as K2JVMCompilerArguments).classpath)
-            Assert.assertEquals("-Xmulti-platform", compilerSettings!!.additionalArguments)
+            Assert.assertEquals("-version", compilerSettings!!.additionalArguments)
         }
     }
 

idea/src/org/jetbrains/kotlin/idea/facet/facetUtils.kt

@@ -176,7 +176,8 @@ val commonUIExposedFields = listOf(
 )
 private val commonUIHiddenFields = listOf(
     CommonCompilerArguments::pluginClasspaths.name,
-    CommonCompilerArguments::pluginOptions.name
+    CommonCompilerArguments::pluginOptions.name,
+    CommonCompilerArguments::multiPlatform.name
 )
 private val commonPrimaryFields = commonUIExposedFields + commonUIHiddenFields