Rename: @JvmName support

#KT-8044 Fixed
 #KT-9432 Fixed

compiler/frontend.java/src/org/jetbrains/kotlin/load/kotlin/PackagePartClassUtils.kt

@@ -19,6 +19,7 @@ package org.jetbrains.kotlin.load.kotlin
 import com.intellij.openapi.util.io.FileUtil
 import com.intellij.openapi.vfs.VirtualFile
 import org.jetbrains.annotations.TestOnly
+import org.jetbrains.kotlin.idea.KotlinFileType
 import org.jetbrains.kotlin.load.java.JvmAbi
 import org.jetbrains.kotlin.name.FqName
 import org.jetbrains.kotlin.name.Name
@@ -45,6 +46,15 @@ object PackagePartClassUtils {
             else
                 "_$str"
 
+    private @JvmStatic fun decapitalizeAsJavaClassName(str: String): String =
+            // NB use Locale.ENGLISH so that build is locale-independent.
+            // See Javadoc on java.lang.String.toUpperCase() for more details.
+            when {
+                Character.isJavaIdentifierStart(str[0]) -> str.substring(0, 1).toLowerCase(Locale.ENGLISH) + str.substring(1)
+                str[0] == '_' -> str.substring(1)
+                else -> str
+            }
+
     @TestOnly
     @JvmStatic fun getDefaultPartFqName(facadeClassFqName: FqName, file: VirtualFile): FqName =
             getPackagePartFqName(facadeClassFqName.parent(), file.name)
@@ -68,4 +78,10 @@ object PackagePartClassUtils {
     @JvmStatic fun getFilePartShortName(fileName: String): String =
             getPartClassName(FileUtil.getNameWithoutExtension(fileName))
 
+    @JvmStatic fun getFileNameByFacadeName(facadeClassName: String): String? {
+        if (!facadeClassName.endsWith(PART_CLASS_NAME_SUFFIX)) return null
+        val baseName = facadeClassName.substring(0, facadeClassName.length - PART_CLASS_NAME_SUFFIX.length)
+        if (baseName == "_") return null
+        return "${decapitalizeAsJavaClassName(baseName)}.${KotlinFileType.EXTENSION}"
+    }
 }