Fix ctrl click to open file on windows (#12294)

There were two issues:
1. the `ModifiersChanged` event was never emitted on windows.
macOS, x11 and wayland have separate events for this, while on windows
they are sent via the usual `keyup` and `keydown` events, but
`parse_keydown_msg_keystroke` just ignored them.
2. the word segmenting regex didn't include '\' so paths weren't
correctly detected

fixes https://github.com/zed-industries/zed/issues/12321

Release Notes:

- N/A