Sanitize names for script class files

Use the same process that is done for package parts in the JVM back-end, except
adding the "Kt" suffix

 #KT-15225 Fixed

compiler/tests/org/jetbrains/kotlin/codegen/ScriptGenTest.kt

@@ -90,6 +90,13 @@ class ScriptGenTest : CodegenTestCase() {
         assertEquals(239, invoke as Int / 2)
     }
 
+    fun testNameSanitation() {
+        setUpEnvironment("scriptCustom/1#@2.kts")
+
+        val aClass = generateClass("_1__2")
+        assertEquals("OK", aClass.getDeclaredMethod("getResult")(aClass.newInstance()))
+    }
+
     private fun setUpEnvironment(sourcePath: String) {
         setUpEnvironment(listOf(sourcePath))
     }