JS: add checker to detect non-external declarations in files marked by JsModule or JsQualifier annotation

js/js.translator/testData/box/jsModule/externalPackage.kt

@@ -1,3 +1,4 @@
+// FILE: a.kt
 // MODULE_KIND: AMD
 @file:JsModule("lib")
 package foo
@@ -24,6 +25,9 @@ external val bar: Int = definedExternally
 
 external var mbar: Int = definedExternally
 
+// FILE: b.kt
+package foo
+
 fun box(): String {
     val a = A(23)
     assertEquals(23, a.x)

js/js.translator/testData/box/jsModule/externalPackagePlain.kt

@@ -1,3 +1,4 @@
+// FILE: a.kt
 @file:JsModule("lib")
 @file:JsNonModule
 package foo
@@ -24,6 +25,9 @@ external val bar: Int = definedExternally
 
 external var mbar: Int = definedExternally
 
+// FILE: b.kt
+package foo
+
 fun box(): String {
     val a = A(23)
     assertEquals(23, a.x)

js/js.translator/testData/box/jsModule/externalPackageUmdFallback.kt

@@ -1,3 +1,4 @@
+// FILE: a.kt
 // MODULE_KIND: UMD
 // NO_JS_MODULE_SYSTEM
 @file:JsModule("lib")
@@ -22,6 +23,9 @@ external val bar: Int = definedExternally
 
 external var mbar: Int = definedExternally
 
+// FILE: b.kt
+package foo
+
 fun box(): String {
     val a = A(23)
     assertEquals(23, a.x)