[JS IR] Preparing for introducing sourcemap as another compilation output

* Rename `JsCode` to `CompilationOutputs`.
* Rename members of CompilerResult.

#KT-46551 In Progress

compiler/cli/cli-js/src/org/jetbrains/kotlin/cli/js/K2JsIrCompiler.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -284,8 +284,8 @@ class K2JsIrCompiler : CLICompiler<K2JSCompilerArguments>() {
                 ),
             )
 
-            val jsCode = if (arguments.irDce && !arguments.irDceDriven) compiledModule.dceJsCode!! else compiledModule.jsCode!!
-            outputFile.writeText(jsCode.mainModule)
+            val jsCode = if (arguments.irDce && !arguments.irDceDriven) compiledModule.outputsAfterDce!! else compiledModule.outputs!!
+            outputFile.writeText(jsCode.jsCode)
             jsCode.dependencies.forEach { (name, content) ->
                 outputFile.resolveSibling("$name.js").writeText(content)
             }

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/compiler.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2018 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -27,12 +27,12 @@ import org.jetbrains.kotlin.library.resolver.KotlinLibraryResolveResult
 import org.jetbrains.kotlin.name.FqName
 
 class CompilerResult(
-    val jsCode: JsCode?,
-    val dceJsCode: JsCode?,
+    val outputs: CompilationOutputs?,
+    val outputsAfterDce: CompilationOutputs?,
     val tsDefinitions: String? = null
 )
 
-class JsCode(val mainModule: String, val dependencies: Iterable<Pair<String, String>> = emptyList())
+class CompilationOutputs(val jsCode: String, val dependencies: Iterable<Pair<String, String>> = emptyList())
 
 fun compile(
     project: Project,
@@ -174,5 +174,5 @@ fun generateJsCode(
     jsPhases.invokeToplevel(PhaseConfig(jsPhases), context, listOf(moduleFragment))
 
     val transformer = IrModuleToJsTransformer(context, null, true, nameTables)
-    return transformer.generateModule(listOf(moduleFragment)).jsCode!!.mainModule
+    return transformer.generateModule(listOf(moduleFragment)).outputs!!.jsCode
 }

compiler/ir/backend.js/src/org/jetbrains/kotlin/ir/backend/js/transformers/irToJs/IrModuleToJsTransformer.kt

@@ -1,12 +1,12 @@
 /*
- * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
 package org.jetbrains.kotlin.ir.backend.js.transformers.irToJs
 
 import org.jetbrains.kotlin.ir.backend.js.CompilerResult
-import org.jetbrains.kotlin.ir.backend.js.JsCode
+import org.jetbrains.kotlin.ir.backend.js.CompilationOutputs
 import org.jetbrains.kotlin.ir.backend.js.JsIrBackendContext
 import org.jetbrains.kotlin.ir.backend.js.eliminateDeadDeclarations
 import org.jetbrains.kotlin.ir.backend.js.export.ExportModelGenerator
@@ -72,7 +72,7 @@ class IrModuleToJsTransformer(
         return CompilerResult(jsCode, dceJsCode, dts)
     }
 
-    private fun generateWrappedModuleBody(modules: Iterable<IrModuleFragment>, exportedModule: ExportedModule, namer: NameTables): JsCode {
+    private fun generateWrappedModuleBody(modules: Iterable<IrModuleFragment>, exportedModule: ExportedModule, namer: NameTables): CompilationOutputs {
         if (multiModule) {
 
             val refInfo = buildCrossModuleReferenceInfo(modules)
@@ -104,9 +104,9 @@ class IrModuleToJsTransformer(
                 )
             }.reversed()
 
-            return JsCode(mainModule, dependencies)
+            return CompilationOutputs(mainModule, dependencies)
         } else {
-            return JsCode(
+            return CompilationOutputs(
                 generateWrappedModuleBody2(
                     modules,
                     emptyList(),