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

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

@@ -0,0 +1,14 @@
+// DONT_TARGET_EXACT_BACKEND: JS
+// ES_MODULES
+package foo
+
+@JsModule("./externalFunctionNameClash.mjs")
+external fun foo(y: Int): Int = definedExternally
+
+fun foo(y: String): String = y + "K"
+
+fun box(): String {
+    val foo10 = foo(10)
+    if (foo10 != 33) return "Fail: $foo10"
+    return "OK"
+}