test removing dollar for objects out of system (#20242)

* test removing dollar for objects out of system

* test & fixes

* fix bootstrap

* use nimPreviewSlimSystem, test stdlib category

* fix test

lib/pure/asyncfutures.nim

@@ -11,6 +11,9 @@ import os, tables, strutils, times, heapqueue, options, deques, cstrutils
 
 import system/stacktraces
 
+when defined(nimPreviewSlimSystem):
+  import std/objectdollar # for StackTraceEntry
+
 # TODO: This shouldn't need to be included, but should ideally be exported.
 type
   CallbackFunc = proc () {.closure, gcsafe.}