[JS IR] Generate jsClass function inside the compiler instead of relying on declaration inside stdlib

We want to make its type parameter reified to do it we have to make it inline and non-external.
But we don't want to inline it in call sites and want prevent using it anywhere except places generated by the compiler.
In user code, including stdlib, we should use `K::class.js` instead.
Separately we have to intrinsify `K::class.js` to reduce overhead.

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

@@ -17,11 +17,9 @@ import org.jetbrains.kotlin.ir.declarations.IrSimpleFunction
 import org.jetbrains.kotlin.ir.declarations.impl.IrExternalPackageFragmentImpl
 import org.jetbrains.kotlin.ir.descriptors.IrBuiltIns
 import org.jetbrains.kotlin.ir.symbols.IrSimpleFunctionSymbol
-import org.jetbrains.kotlin.ir.types.IrType
-import org.jetbrains.kotlin.ir.types.defaultType
+import org.jetbrains.kotlin.ir.types.*
 import org.jetbrains.kotlin.ir.types.impl.IrSimpleTypeBuilder
 import org.jetbrains.kotlin.ir.types.impl.buildSimpleType
-import org.jetbrains.kotlin.ir.types.isLong
 import org.jetbrains.kotlin.ir.util.constructors
 import org.jetbrains.kotlin.ir.util.findDeclaration
 import org.jetbrains.kotlin.ir.util.kotlinPackageFqn
@@ -169,7 +167,9 @@ class JsIntrinsics(private val irBuiltIns: IrBuiltIns, val context: JsIrBackendC
     val jsGetContinuation = getInternalFunction("getContinuation")
     val jsGetKClass = getInternalWithoutPackage("getKClass")
     val jsGetKClassFromExpression = getInternalWithoutPackage("getKClassFromExpression")
-    val jsClass = getInternalFunction("jsClass")
+
+    private val jsClassClassSymbol = getInternalClassWithoutPackage("kotlin.js.JsClass")
+    val jsClass = defineJsClassIntrinsic().symbol
 
     val jsNumberRangeToNumber = getInternalFunction("numberRangeToNumber")
     val jsNumberRangeToLong = getInternalFunction("numberRangeToLong")
@@ -448,6 +448,21 @@ class JsIntrinsics(private val irBuiltIns: IrBuiltIns, val context: JsIrBackendC
         }
     }
 
+    private fun defineJsClassIntrinsic(): IrSimpleFunction {
+        return irFactory.addFunction(externalPackageFragment) {
+            name = Name.identifier("jsClass")
+            origin = JsLoweredDeclarationOrigin.JS_INTRINSICS_STUB
+            isInline = true
+        }.apply {
+            val typeParameter = addTypeParameter {
+                name = Name.identifier("T")
+                isReified = true
+                superTypes += irBuiltIns.anyType
+            }
+            returnType = jsClassClassSymbol.typeWithParameters(listOf(typeParameter))
+        }
+    }
+
     private fun unOp(name: String, returnType: IrType = irBuiltIns.anyNType) =
         irBuiltIns.run { defineOperator(name, returnType, listOf(anyNType)) }
 

libraries/stdlib/js-ir/src/kotlin/jsClass_js-ir.kt

@@ -1,8 +0,0 @@
-/*
- * Copyright 2010-2020 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 kotlin.js
-
-internal inline fun <reified T : Any> jsClass(): JsClass<T> = throw NotImplementedError("Implemented as intrinsic")