This patch fixes stdin read hanging on user input when switching tty
mode on Windows
Fixes #21111
On Windows, when switching from line to raw mode:
- Cancel ongoing console read by writing a return keypress to its input
buffer. This blocks the main thread until any ongoing read has been
cancelled to prevent interference with the screen state.
- On the read thread, restore the cursor position to where it was before
writing the enter, undoing its effect on the screen state.
- Restart reading and notify the main thread.
