[Wasm] Use Wasm GC arrays instead of JS arrays

JS arrays was a workaround for lack of arrays in Firefox Wasm GC prototype
Now with V8 as a test runner we can use proper arrays

libraries/tools/kotlin-stdlib-gen/src/generators/GenerateStandardLib.kt

@@ -72,7 +72,7 @@ fun main(args: Array<String>) {
         targetDir.resolve("_${source.name.capitalize()}$platformSuffix.kt")
     }
 
-    targetBaseDirs[KotlinTarget.WASM]?.let { generateWasmOps(it) }
+    targetBaseDirs[KotlinTarget.WASM]?.let { generateWasmBuiltIns(it) }
 }
 
 fun File.resolveExistingDir(subpath: String) = resolve(subpath).also { it.requireExistingDir() }

libraries/tools/kotlin-stdlib-gen/src/generators/GenerateWasmOps.kt

@@ -8,16 +8,27 @@ package generators
 import org.jetbrains.kotlin.wasm.ir.WasmOp
 import templates.COMMON_AUTOGENERATED_WARNING
 import templates.COPYRIGHT_NOTICE
+import templates.PrimitiveType
 import java.io.File
 import java.io.FileWriter
 
+
+fun generateWasmBuiltIns(targetDir: File) {
+    generateWasmOps(targetDir)
+    generateWasmArrays(targetDir)
+}
+
+fun FileWriter.generateStandardWasmInternalHeader() {
+    appendLine(COPYRIGHT_NOTICE)
+    appendLine("package kotlin.wasm.internal")
+    appendLine()
+    appendLine(COMMON_AUTOGENERATED_WARNING)
+    appendLine()
+}
+
 fun generateWasmOps(targetDir: File) {
     FileWriter(targetDir.resolve("_WasmOp.kt")).use { writer ->
-        writer.appendLine(COPYRIGHT_NOTICE)
-        writer.appendLine("package kotlin.wasm.internal")
-        writer.appendLine()
-        writer.appendLine(COMMON_AUTOGENERATED_WARNING)
-        writer.appendLine()
+        writer.generateStandardWasmInternalHeader()
         writer.appendLine(
             """
             @ExcludedFromCodegen
@@ -38,4 +49,46 @@ fun generateWasmOps(targetDir: File) {
             """.trimIndent()
         )
     }
+}
+
+fun generateWasmArrays(targetDir: File) {
+    FileWriter(targetDir.resolve("_WasmArrays.kt")).use { writer ->
+        writer.generateStandardWasmInternalHeader()
+
+        writer.appendLine(wasmArrayForType("Any", true))
+        writer.appendLine(wasmArrayForType("Boolean", false))
+        PrimitiveType.numericPrimitives.sortedBy { it.capacity }.forEach { primitive ->
+            writer.appendLine(wasmArrayForType(primitive.name, false))
+        }
+    }
+}
+
+fun wasmArrayForType(klass: String, isNullable: Boolean): String {
+    val type = klass + if (isNullable) "?" else ""
+    val name = "Wasm${klass}Array"
+    return """
+            @WasmArrayOf($klass::class, isNullable = $isNullable)
+            internal class $name(size: Int) {
+                @WasmOp(WasmOp.ARRAY_GET)
+                fun get(index: Int): $type =
+                    implementedAsIntrinsic
+    
+                @WasmOp(WasmOp.ARRAY_SET)
+                fun set(index: Int, value: $type): Unit =
+                    implementedAsIntrinsic
+    
+                @WasmOp(WasmOp.ARRAY_LEN)
+                fun len(): Int =
+                    implementedAsIntrinsic
+            }
+    
+            internal inline fun $name.fill(size: Int, init: (Int) -> $type) {
+                var i = 0
+                while (i < size) {
+                    set(i, init(i))
+                    i++
+                }
+            }
+            
+            """.trimIndent()
 }