[Wasm] Add an option to dump declaration IR sizes to file

compiler/cli/cli-common/src/org/jetbrains/kotlin/cli/common/arguments/K2JSCompilerArguments.kt

@@ -308,6 +308,20 @@ class K2JSCompilerArguments : CommonCompilerArguments() {
             field = value
         }
 
+    @Argument(
+        value = "-Xir-dump-declaration-ir-sizes-to-file",
+        valueDescription = "<path>",
+        description = "Dump the IR size of each declaration to a file. " +
+                "The format will be chosen automatically depending on the file extension. " +
+                "Supported output formats include JSON for .json, JS const initialized with a plain object containing information for .js, " +
+                "and plain text for all other file types."
+    )
+    var irDceDumpDeclarationIrSizesToFile: String? = null
+        set(value) {
+            checkFrozen()
+            field = value
+        }
+
     @Argument(value = "-Xir-property-lazy-initialization", description = "Perform lazy initialization for properties")
     var irPropertyLazyInitialization = true
         set(value) {

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

@@ -44,6 +44,7 @@ import org.jetbrains.kotlin.incremental.js.IncrementalNextRoundChecker
 import org.jetbrains.kotlin.incremental.js.IncrementalResultsConsumer
 import org.jetbrains.kotlin.ir.backend.js.*
 import org.jetbrains.kotlin.ir.backend.js.codegen.JsGenerationGranularity
+import org.jetbrains.kotlin.ir.backend.js.dce.dumpDeclarationIrSizesIfNeed
 import org.jetbrains.kotlin.ir.backend.js.ic.*
 import org.jetbrains.kotlin.ir.backend.js.transformers.irToJs.CompilationOutputsBuilt
 import org.jetbrains.kotlin.ir.backend.js.transformers.irToJs.IrModuleToJsTransformer
@@ -354,6 +355,8 @@ class K2JsIrCompiler : CLICompiler<K2JSCompilerArguments>() {
                     eliminateDeadDeclarations(allModules, backendContext)
                 }
 
+                dumpDeclarationIrSizesIfNeed(arguments.irDceDumpDeclarationIrSizesToFile, allModules)
+
                 val generateSourceMaps = configuration.getBoolean(JSConfigurationKeys.SOURCE_MAP)
 
                 val res = compileWasm(