JS unittest stacktrace fix, cleanup js repr and inclrtl includes (#14168)

tests/js/tunittest_error.nim

@@ -0,0 +1,22 @@
+discard """
+  exitcode: 1
+  outputsub: "[FAILED] with exception"
+"""
+
+import unittest
+
+proc ddd() =
+  raise newException(IOError, "didn't do stuff")
+
+proc ccc() =
+  ddd()
+
+proc bbb() =
+  ccc()
+
+proc aaa() =
+  bbb()
+
+test "with exception":
+  check 3 == 3
+  aaa()