JS: fix parsing of object literals in js() function.

Also, fix generation of source maps of content of js() function.

See KT-19794

js/js.translator/testData/lineNumbers/jsCode.kt

@@ -0,0 +1,8 @@
+fun foo() {
+    var x = "foo"
+    println("before: $x")
+    js("console.log('js' + x);")
+    println("after: $x")
+}
+
+// LINES: 6 2 2 3 3 4 4 5 5