[JS IR BE] Codegen class model refactorings

Reduce JsScope usage

js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/JsClassModel.kt

@@ -18,6 +18,5 @@ package org.jetbrains.kotlin.js.backend.ast
 
 class JsClassModel(val name: JsName, val superName: JsName?) {
     val interfaces: MutableSet<JsName> = mutableSetOf()
-    val preDeclarationBlock = JsGlobalBlock() // TODO only used in IR backend => hide from current backend
     val postDeclarationBlock = JsGlobalBlock()
 }

js/js.ast/src/org/jetbrains/kotlin/js/backend/ast/JsName.java

@@ -20,11 +20,15 @@ public class JsName extends HasMetadata implements Symbol {
   /**
    * @param ident the unmangled ident to use for this name
    */
-  JsName(@NotNull String ident, boolean temporary) {
+  public JsName(@NotNull String ident, boolean temporary) {
     this.ident = ident;
     this.temporary = temporary;
   }
 
+  public JsName(@NotNull String ident) {
+    this(ident, false);
+  }
+
   public boolean isTemporary() {
     return temporary;
   }