protocols: add support for text-input-v1

[ammen99]

Fixes #1789

Tested briefly with weston-editor and google chrome, which needs --enable-wayland-ime on the command line to work.

If someone else needs this, please test :)

[akliuxingyuan]

Thank you very much for adding tiv1 support, I can compose and commit Chinese characters, but it doesn't draw a rectangle for candidate list.

[ammen99]

Thank you very much for adding tiv1 support, I can compose and commit Chinese characters, but it doesn't draw a rectangle for candidate list.

Yes that requires a little bit more work, but I don't plan to add this myself. If you (or someone else) is interested in working on this, let me know and I can explain what is necessary.