[JS IR BE] Add JsExport annotations

js/js.translator/testData/box/propertyAccess/accessorsWithJsName.kt

@@ -11,6 +11,7 @@ class A {
         }
 }
 
+@JsExport
 val A.z: Int
     @JsName("getZ_") get() = 42
 

js/js.translator/testData/box/propertyAccess/staticAccessorsWithJsName.kt

@@ -1,8 +1,10 @@
 // EXPECTED_REACHABLE_NODES: 1288
 
+@JsExport
 val x: Int
     @JsName("getX_") get() = 23
 
+@JsExport
 var y: Int = 0
     @JsName("getY_") get() = field + 10
     @JsName("setY_") set(value) {