The previous behavior was to always treat ctrl-alt as altgr on Windows,
this has been done to better support altgr through a VNC session,
but this is very unintuitive when you don't need this behavior.
ref: #472
Dead key processing respects the
`send_composed_key_when_left_alt_is_pressed` and
`send_composed_key_when_right_alt_is_pressed` options.
See doc changes included in this commit for more info.
refs: https://github.com/wez/wezterm/issues/410
This adopts a similar technique to that used to pass the wezterm
config to the term crate, but this time it is for passing it to
the window crate.
The use_ime option has been ported over to this new mechanism.
