Add script flag to kotlin.Metadata

This will allow to distinguish compiled scripts from ordinary classes in the
compiler, reflection, IDE, etc.

 #KT-13382 Fixed

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/java/JvmAnnotationNames.java

@@ -36,6 +36,7 @@ public final class JvmAnnotationNames {
 
     public static final int METADATA_MULTIFILE_PARTS_INHERIT_FLAG = 1 << 0;
     public static final int METADATA_PRE_RELEASE_FLAG = 1 << 1;
+    public static final int METADATA_SCRIPT_FLAG = 1 << 2;
 
     public static final Name DEFAULT_ANNOTATION_MEMBER_NAME = Name.identifier("value");
 

core/descriptor.loader.java/src/org/jetbrains/kotlin/load/kotlin/header/KotlinClassHeader.kt

@@ -71,5 +71,8 @@ class KotlinClassHeader(
     val isPreRelease: Boolean
         get() = (extraInt and JvmAnnotationNames.METADATA_PRE_RELEASE_FLAG) != 0
 
+    val isScript: Boolean
+        get() = (extraInt and JvmAnnotationNames.METADATA_SCRIPT_FLAG) != 0
+
     override fun toString() = "$kind version=$metadataVersion"
 }

core/runtime.jvm/src/kotlin/Metadata.kt

@@ -61,6 +61,7 @@ internal annotation class Metadata(
          *
          * 0 - this is a multi-file class facade or part, compiled with `-Xmultifile-parts-inherit`.
          * 1 - this class file is compiled by a pre-release version of Kotlin and is not visible to release versions.
+         * 2 - this class file is a compiled Kotlin script source file (.kts).
          */
         val xi: Int = 0
 )