Problem:
On Windows, channel jobs inherit Nvim's stdio, so a background job
writing to CON (e.g. gutentags) draws onto the TUI and stays until
redraw.
Solution:
Give Windows job stdin/stderr libuv-created pipes (UV_CREATE_PIPE)
instead of inherited fds, so libuv spawns the child with
CREATE_NO_WINDOW and CON writes no longer leak onto the TUI.
(cherry picked from commit 39e9c1754a)
61765b97fe