Automatic deref for everything but pointers in asm/emit (#8891)

Fixes #7249

tests/js/t7249.nim

@@ -0,0 +1,21 @@
+discard """
+  output: '''
+a -> 2
+a <- 2
+'''
+"""
+
+import jsffi
+
+var a = JsAssoc[cstring, int]{a: 2}
+
+for z, b in a:
+  echo z, " -> ", b
+
+proc f =
+  var a = JsAssoc[cstring, int]{a: 2}
+
+  for z, b in a:
+    echo z, " <- ", b
+
+f()