JS: several bugfixes in incremental compilation

1. Fix exported packages sometimes being mixed up
2. Fix metadata losing package fragments sometimes
3. Don't serialize empty packages to .meta.js
4. Preserve order of package fragments in .meta.js
5. In IC tests, compare textual representation of metadata rather
   than binary representation

js/js.translator/testData/box/incremental/packagesWithSameName.kt

@@ -0,0 +1,31 @@
+// EXPECTED_REACHABLE_NODES: 1126
+// MODULE: lib
+// FILE: a.kt
+package a.p
+
+fun foo() = "foo"
+
+// FILE: b1.kt
+// RECOMPILE
+package b.p
+
+fun bar() = "bar"
+
+// FILE: b2.kt
+package b.p
+
+fun baz() = "baz"
+
+// MODULE: main(lib)
+// FILE: main.kt
+import a.p.*
+import b.p.*
+
+fun box(): String {
+    val r = foo() + bar() + baz()
+
+    if (r != "foobarbaz") return "fail: $r"
+
+    return "OK"
+}
+