StringStream & more stdlib modules support for JS/NimScript (#14095)

* StringStream & more stdlib modules support for JS/NimScript

* change back pegs test in line with #14134

tests/js/tstdlib_imports.nim

@@ -0,0 +1,71 @@
+discard """
+  action: compile
+"""
+
+{.warning[UnusedImport]: off.}
+
+import std/[
+  # Core:
+  bitops, typetraits, lenientops, macros, volatile, typeinfo,
+  # fails: endians, rlocks
+  # works but shouldn't: cpuinfo, locks
+
+  # Algorithms:
+  algorithm, sequtils,
+  
+  # Collections:
+  critbits, deques, heapqueue, intsets, lists, options, sets,
+  sharedlist, tables,
+  # fails: sharedtables
+
+  # Strings:
+  cstrutils, editdistance, wordwrap, parseutils, ropes,
+  pegs, punycode, strformat, strmisc, strscans, strtabs,
+  strutils, unicode, unidecode,
+  # fails: encodings
+
+  # Time handling:
+  monotimes, times,
+
+  # Generic operator system services:
+  os, streams,
+  # fails: distros, dynlib, marshal, memfiles, osproc, terminal
+
+  # Math libraries:
+  complex, math, mersenne, random, rationals, stats, sums,
+  # works but shouldn't: fenv
+
+  # Internet protocols:
+  cookies, httpcore, mimetypes, uri,
+  # fails: asyncdispatch, asyncfile, asyncftpclient, asynchttpserver,
+  # asyncnet, cgi, httpclient, nativesockets, net, selectors, smtp
+  # works but shouldn't test: asyncstreams, asyncfutures
+  
+  # Threading:
+  # fails: threadpool
+
+  # Parsers:
+  htmlparser, json, lexbase, parsecfg, parsecsv, parsesql, parsexml,
+  # fails: parseopt
+
+  # XML processing:
+  xmltree, xmlparser,
+
+  # Generators:
+  htmlgen,
+
+  # Hashing:
+  base64, hashes,
+  # fails: md5, oids, sha1
+
+  # Miscellaneous:
+  colors, logging, sugar, unittest, varints,
+  # fails: browsers, coro
+  # works but shouldn't: segfaults
+
+  # Modules for JS backend:
+  asyncjs, dom, jsconsole, jscore, jsffi,
+
+  # Unlisted in lib.html:
+  decls, compilesettings, with, wrapnils
+]