* Merge a bunch of related state together into TerminalMode. Windows
sometimes follows the same path as posix via ansi_escape_codes,
sometimes not.
* Use a different thread entry point for Windows API but share the same
entry point on Windows when the terminal is in ansi_escape_codes mode.
* Only clear the terminal when the stderr lock is held.
* Don't try to clear the terminal when nothing has been written yet.
* Don't try to clear the terminal in IPC mode.
* Fix size detection logic bug under error conditions.
3a3d2187f9