Use internal names in multifile class metadata

To reuse the strings already existing in the constant pool of the class file

idea/idea-analysis/src/org/jetbrains/kotlin/idea/decompiler/DecompiledUtils.kt

@@ -89,9 +89,6 @@ public fun findMultifileClassParts(file: VirtualFile, multifileClass: KotlinJvmB
     val partsFinder = DirectoryBasedClassFinder(file.parent!!, packageFqName)
     val partNames = multifileClass.classHeader.filePartClassNames ?: return emptyList()
     return partNames.map {
-        partsFinder.findKotlinClass(ClassId(packageFqName, Name.identifier(it)))
+        partsFinder.findKotlinClass(ClassId(packageFqName, Name.identifier(it.substringAfterLast('/'))))
     }.filterNotNull()
 }
-
-public fun readMultifileClassPartHeaders(file: VirtualFile, multifileClass: KotlinJvmBinaryClass): List<KotlinClassHeader> =
-        findMultifileClassParts(file, multifileClass).map { it.classHeader }

idea/idea-analysis/src/org/jetbrains/kotlin/idea/decompiler/stubBuilder/clsStubBuilding.kt

@@ -80,7 +80,7 @@ fun createMultifileClassStub(
         components: ClsStubBuilderComponents
 ): KotlinFileStubImpl {
     val packageFqName = facadeFqName.parent()
-    val partNames = multifileClass.classHeader.filePartClassNames?.asList()
+    val partNames = multifileClass.classHeader.filePartClassNames?.asList()?.map { it.substringAfterLast('/') }
     val fileStub = KotlinFileStubForIde.forMultifileClassStub(facadeFqName, partNames, packageFqName.isRoot)
     setupFileStub(fileStub, packageFqName)
     for (partFile in partFiles) {