fix(channel): support :detach, :restart on Windows #37977

fix: allocate hidden console for detached server

Starting the server with UV_PROCESS_DETACHED results in DETACHED_PROCESS, leaving the child without a console. Without a console:

CONIN$ / CONOUT$ cannot resolve, causing channel_from_stdio to fail.

ConPTY cannot attach, breaking :terminal.

This patch allocates a hidden console via AllocConsole() when the server has none, restoring working stdio and enabling ConPTY.

Also updates os_set_cloexec to clear HANDLE_FLAG_INHERIT on the RPC pipe
handles, matching the Unix F_DUPFD_CLOEXEC behavior.

test/functional/testterm.lua

@@ -8,6 +8,7 @@
 --    - NOTE: Only use this if your test actually needs the full lifecycle/capabilities of the
 --    builtin Nvim TUI. Most tests should just use `Screen.new()` directly, or plain old API calls.
 
+local t = require('test.testutil')
 local n = require('test.functional.testnvim')()
 local Screen = require('test.functional.ui.screen')
 
@@ -207,4 +208,17 @@ function M.setup_child_nvim(args, opts)
   return M.setup_screen(opts.extra_rows, argv, opts.cols, env)
 end
 
+--- FIXME: On Windows spaces at the end of a screen line may have wrong attrs.
+--- Remove this function when that's fixed.
+---
+--- @param screen test.functional.ui.screen
+--- @param s string
+function M.screen_expect(screen, s)
+  if t.is_os('win') then
+    s = s:gsub(' *%} +%|\n', '{MATCH: *}}{MATCH: *}|\n')
+    s = s:gsub('%}%^ +%|\n', '{MATCH:[ ^]*}}{MATCH:[ ^]*}|\n')
+  end
+  screen:expect(s)
+end
+
 return M