ansi_c: support rawWrite(cstderr|cstdout, s) in js, nodejs, vm

[timotheecour]

followup on #16016.

with this PR:

• rawWrite(cstderr|cstdout, s) now works in js, nodejs, vm (and vm+js, vm+nodejs)
  this is useful in itself (in particular writing without newline for vm, unlike echo, or writing to stderr in vm/nodejs/js), and also avoids having to special case a lot of existing code using rawWrite for those backends.

• writeStackTrace writes to stderr for js,nodejs, consistently with docs for writeStackTrace and with c backend

• --panics:on now works better with js/nodejs (previously, would give stderr not defined)

example

proc fn() =
  writeStackTrace()
fn()

from system/ansi_c import rawWrite, cstderr, cstdout
rawWrite(cstderr, "ok1")
rawWrite(cstderr, "ok2\n")
rawWrite(cstdout, "ok3")
rawWrite(cstdout, "ok4\n")

doAssertRaises(AssertionDefect):
  doAssert false, "foo"

nim r --panics main:

Traceback (most recent call last)
/Users/timothee/git_clone/nim/timn/tests/nim/all/t11366.nim(7) t11366
/Users/timothee/git_clone/nim/timn/tests/nim/all/t11366.nim(6) fn
ok1ok2
ok3ok4
Traceback (most recent call last)
/Users/timothee/git_clone/nim/timn/tests/nim/all/t11366.nim(15) t11366
/Users/timothee/git_clone/nim/Nim_prs/lib/system/assertions.nim(30) failedAssertImpl
/Users/timothee/git_clone/nim/Nim_prs/lib/system/assertions.nim(23) raiseAssert
/Users/timothee/git_clone/nim/Nim_prs/lib/system/fatal.nim(45) sysFatal
/Users/timothee/git_clone/nim/Nim_prs/lib/system/fatal.nim(33) sysFatal
Error: unhandled exception: /Users/timothee/git_clone/nim/timn/tests/nim/all/t11366.nim(15, 43) `false` foo [AssertionDefect]

nim r -b:js --panics -d:nodejs main
almost same:

Traceback (most recent call last)
/Users/timothee/git_clone/nim/timn/tests/nim/all/t11366.nim(7) at module t11366
/Users/timothee/git_clone/nim/timn/tests/nim/all/t11366.nim(6) at t11366.fn
ok1ok2
ok3ok4
Traceback (most recent call last)
/Users/timothee/git_clone/nim/timn/tests/nim/all/t11366.nim(15) at module t11366
/Users/timothee/git_clone/nim/Nim_prs/lib/system/assertions.nim(30) at assertions.failedAssertImpl
/Users/timothee/git_clone/nim/Nim_prs/lib/system/assertions.nim(23) at assertions.raiseAssert
/Users/timothee/git_clone/nim/Nim_prs/lib/system/fatal.nim(45) at sysFatal.sysFatal
/Users/timothee/git_clone/nim/Nim_prs/lib/system/fatal.nim(33) at sysFatal.sysFatal

nim r -b:js --panics main

in this case it now correctly shows the AssertionDefect error + msg, but later fails for a different reason, because exit isn't defined; this can be fixed and is the same issue as #16074
Another caveat is rawWrite behaves more like some hypothetical rawWriteln

Traceback (most recent call last)
/Users/timothee/git_clone/nim/timn/tests/nim/all/t11366.nim(7) at module t11366
/Users/timothee/git_clone/nim/timn/tests/nim/all/t11366.nim(6) at t11366.fn

ok1
ok2

ok3
ok4

Traceback (most recent call last)
/Users/timothee/git_clone/nim/timn/tests/nim/all/t11366.nim(15) at module t11366
/Users/timothee/git_clone/nim/Nim_prs/lib/system/assertions.nim(30) at assertions.failedAssertImpl
/Users/timothee/git_clone/nim/Nim_prs/lib/system/assertions.nim(23) at assertions.raiseAssert
/Users/timothee/git_clone/nim/Nim_prs/lib/system/fatal.nim(45) at sysFatal.sysFatal
/Users/timothee/git_clone/nim/Nim_prs/lib/system/fatal.nim(33) at sysFatal.sysFatal

Error: unhandled exception: /Users/timothee/git_clone/nim/timn/tests/nim/all/t11366.nim(15, 43) `false` foo [AssertionDefect]

Traceback (most recent call last)
/Users/timothee/git_clone/nim/timn/tests/nim/all/t11366.nim(109) at module t11366
/Users/timothee/git_clone/nim/Nim_prs/lib/system/assertions.nim(23) at assertions.raiseAssert
/Users/timothee/git_clone/nim/Nim_prs/lib/system/fatal.nim(45) at sysFatal.sysFatal
/Users/timothee/git_clone/nim/Nim_prs/lib/system/fatal.nim(33) at sysFatal.sysFatal

Error: unhandled exception: expected raising 'AssertionDefect', instead raised foreign exception by:
doAssert false, "foo" [AssertionDefect]

/Users/timothee/git_clone/nim/timn/build/nimcache/t11366.js:506
    exit(1);
    ^

ReferenceError: exit is not defined
    at sysFatal_218103880 (/Users/timothee/git_clone/nim/timn/build/nimcache/t11366.js:506:5)

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. If you think it is still a valid PR, please rebase it on the latest devel; otherwise it will be closed. Thank you for your contributions.