keyboard support: altgr modifier not recognized

When using non-US layouts, such as the Swiss French layout (`ch fr`), the "altgr" key combos aren't recognised, meaning for example that `` on the Swiss french layout won't produce an `@` char as it should. I imagine this also impact the german layout where `` is supposed to be `@`

On Windows, `` is recognized as `altgr` (I have not tested if this work in Junie), but not on Linux, so currently there are no workaround to type `@` other than switching layouts or copying it from outside the shell Junie is running in.