shiny: add Compose key support for X11
shiny: add Compose key support for X11

Fixes golang/go#16332

Change-Id: Id72fe556380acca6c0cb20af7bda3bcec3783b4e
Reviewed-on: https://go-review.googlesource.com/24881
Reviewed-by: Nigel Tao <58ae08b3356928ff9c67562b4719487d54fe8348@golang.org>

golang/exp,golang/exp,golang/exp