compose handling is broken

Things that does not work:

Alt-compose handling: (Alt + ~) + 'a' -> ã
compose key handling: (compose) + '\'' + 'a' -> á
chinese input handling (win) + (space) to toggle language

We lack a test for "isComposing" on the platforms that have it.

(on windows the O/S handles '~' + 'a' as a dead key, and only inputs the final result )