[K/JS] Add support of compilation with ES-classes

compiler/testData/codegen/box/casts/castToDefinitelyNotNullType.kt

@@ -1,6 +1,6 @@
 // !LANGUAGE: +DefinitelyNonNullableTypes
 // IGNORE_BACKEND: JS
-// IGNORE_BACKEND: JS_IR
+// IGNORE_BACKEND: JS_IR, JS_IR_ES6
 // IGNORE_BACKEND: WASM
 
 fun <T> test(t: T) = t as (T & Any)

compiler/testData/codegen/box/casts/objectToPrimitiveWithAssertion.kt

@@ -1,4 +1,4 @@
-// IGNORE_BACKEND: JS, JS_IR, WASM
+// IGNORE_BACKEND: JS, JS_IR, JS_IR_ES6, WASM
 @Suppress("UNCHECKED_CAST")
 fun <T> f() = 1L as T