[K/JS] Add a test for the ^KT-75606 issue

Merge-request: KT-MR-20438
Merged-by: Artem Kobzar <Artem.Kobzar@jetbrains.com>

Author: JSMonk

plugins/js-plain-objects/compiler-plugin/testData/box/multipleObjectsInTheSameFile.kt

@@ -0,0 +1,41 @@
+// MODULE: lib
+// FILE: lib.kt
+package foo
+
+import kotlinx.js.JsPlainObject
+
+@JsPlainObject
+external interface User {
+    var name: String
+    val age: Int
+}
+
+@JsPlainObject
+external interface Admin {
+    var email: String
+    val level: Int
+}
+
+// MODULE: main(lib)
+// FILE: main.kt
+package foo
+
+fun box(): String {
+    val user = User(name = "Name", age = 10)
+
+    if (user.name != "Name") return "Fail: problem with `name` property"
+    if (user.age != 10) return "Fail: problem with `age` property"
+
+    val userJson = js("JSON.stringify(user)")
+    if (userJson != "{\"name\":\"Name\",\"age\":10}") return "Fail: got the next json: $userJson"
+
+    val admin = Admin(email = "admin@admin.com", level = 0)
+
+    if (admin.email != "admin@admin.com") return "Fail: problem with `email` property"
+    if (admin.level != 0) return "Fail: problem with `level` property"
+
+    val adminJson = js("JSON.stringify(admin)")
+    if (adminJson != "{\"email\":\"admin@admin.com\",\"level\":0}") return "Fail: got the next json: $adminJson"
+
+    return "OK"
+}