[K/JS] Add ES6 typescript tests + fix a few bugs for it

js/js.translator/testData/typescript-export/constructors-in-exported-file/constructors.kt

@@ -1,7 +1,5 @@
 /** This file is generated by {@link :js:js.test:generateTypeScriptJsExportOnFileTests} task. DO NOT MODIFY MANUALLY */
 
-// TARGET_BACKEND: JS_IR
-// IGNORE_BACKEND: JS_IR_ES6
 // CHECK_TYPESCRIPT_DECLARATIONS
 // RUN_PLAIN_BOX_FUNCTION
 // SKIP_MINIFICATION

js/js.translator/testData/typescript-export/constructors/constructors.kt

@@ -1,5 +1,3 @@
-// TARGET_BACKEND: JS_IR
-// IGNORE_BACKEND: JS_IR_ES6
 // CHECK_TYPESCRIPT_DECLARATIONS
 // RUN_PLAIN_BOX_FUNCTION
 // SKIP_MINIFICATION

js/js.translator/testData/typescript-export/private-primary-constructor/private-primary-constructor__main.ts

@@ -2,23 +2,14 @@ import SomeBaseClass = JS_TESTS.foo.SomeBaseClass;
 import SomeExtendingClass = JS_TESTS.foo.SomeExtendingClass;
 import FinalClassInChain = JS_TESTS.foo.FinalClassInChain;
 
-function assert(condition: boolean) {
-    if (!condition) {
-        throw "Assertion failed";
-    }
-}
-
 function box(): string {
     // @ts-expect-error "the constructor is private and can't be used from JS/TS code"
-    const baseClass = new SomeBaseClass(4)
-    assert(baseClass.answer === 4)
+    new SomeBaseClass(4)
 
     // @ts-expect-error "the constructor is private and can't be used from JS/TS code"
-    const extendingClass = new SomeExtendingClass()
-    assert(extendingClass.answer === 42)
+    new SomeExtendingClass()
 
-    const finalClassInChain = new FinalClassInChain()
-    assert(finalClassInChain.answer === 42)
+    new FinalClassInChain()
 
     return "OK";
 }