[JS IR] Support per-file mode and ES modules

js/js.translator/testData/box/esModules/jsModule/interfaces.kt

@@ -0,0 +1,33 @@
+// DONT_TARGET_EXACT_BACKEND: JS
+// ES_MODULES
+// FILE: bar.kt
+@file:JsModule("./interfaces.mjs")
+@file:JsQualifier("foo")
+package foo
+
+external interface Bar {
+    fun ping(): String
+}
+
+// FILE: baz.kt
+@file:JsModule("./interfaces.mjs")
+package boo
+
+external interface Baz {
+    fun pong(): Int
+}
+
+// FILE: root.kt
+@file:JsModule("./interfaces.mjs")
+import foo.Bar
+import boo.Baz
+
+external val bar: Bar
+external val baz: Baz
+
+// FILE: test.kt
+fun box(): String {
+    if (bar.ping() != "ping" || baz.pong() != 194) return "Fail"
+
+    return "OK"
+}