KT-2752: add checkers for inconsistent usage of JsName

js/js.translator/testData/box/multiFile/packageAndMangledMethodDoNotClash.kt

@@ -0,0 +1,15 @@
+// FILE: foo.kt
+package foo
+
+fun bar(x: Int) = x
+
+fun box(): Boolean {
+    assertEquals(23, bar(23))
+    assertEquals(42, foo.bar.x)
+    return true
+}
+
+// FILE: foobar.kt
+package foo.bar
+
+val x = 42

js/js.translator/testData/box/multiFile/packageAndPrivateDeclarationDoNotClash.kt

@@ -0,0 +1,19 @@
+// FILE: foo.kt
+package foo
+
+private fun bar() = 23
+
+private val bar = 42
+
+fun box(): Boolean {
+    assertEquals(23, bar())
+    assertEquals(42, bar)
+    assertEquals(32, foo.bar.x)
+
+    return true
+}
+
+// FILE: foobar.kt
+package foo.bar
+
+val x = 32