Support fun interfaces in kotlinx-metadata

#KT-37421 Fixed

libraries/tools/kotlinp/src/org/jetbrains/kotlin/kotlinp/printers.kt

@@ -946,6 +946,7 @@ private val CLASS_FLAGS_MAP = COMMON_FLAGS_MAP + mapOf(
     Flag.Class.IS_EXTERNAL to "external",
     Flag.Class.IS_EXPECT to "expect",
     Flag.Class.IS_INLINE to "inline",
+    Flag.Class.IS_FUN to "fun",
 
     Flag.Class.IS_CLASS to "class",
     Flag.Class.IS_INTERFACE to "interface",

libraries/tools/kotlinp/test/org/jetbrains/kotlin/kotlinp/test/GenerateKotlinpTests.kt

@@ -7,7 +7,7 @@ package org.jetbrains.kotlin.kotlinp.test
 
 import org.jetbrains.kotlin.generators.tests.generator.testGroup
 
-fun main(args: Array<String>) {
+fun main() {
     System.setProperty("java.awt.headless", "true")
 
     testGroup("libraries/tools/kotlinp/test", "libraries/tools/kotlinp/testData") {

libraries/tools/kotlinp/test/org/jetbrains/kotlin/kotlinp/test/KotlinpTestGenerated.java

@@ -38,6 +38,11 @@ public class KotlinpTestGenerated extends AbstractKotlinpTest {
         runTest("libraries/tools/kotlinp/testData/Contracts.kt");
     }
 
+    @TestMetadata("FunInterface.kt")
+    public void testFunInterface() throws Exception {
+        runTest("libraries/tools/kotlinp/testData/FunInterface.kt");
+    }
+
     @TestMetadata("Lambda.kt")
     public void testLambda() throws Exception {
         runTest("libraries/tools/kotlinp/testData/Lambda.kt");

libraries/tools/kotlinp/testData/FunInterface.kt

@@ -0,0 +1,3 @@
+fun interface F {
+    fun String.f(x: Int)
+}

libraries/tools/kotlinp/testData/FunInterface.txt

@@ -0,0 +1,13 @@
+// F.class
+// ------------------------------------------
+public abstract fun interface F : kotlin/Any {
+
+  // signature: f(Ljava/lang/String;I)V
+  public abstract fun kotlin/String.f(x: kotlin/Int): kotlin/Unit
+
+  // module name: test-module
+}
+// META-INF/test-module.kotlin_module
+// ------------------------------------------
+module {
+}