[ozone/wayland] Implement basic keyboard handling support
CL implements basic keyboard support on Ozone's Wayland backend as well
as some testing.
Modifiers work as follows: when the wayland compositor calls out the
client hook notifying of a modifier key state changed, we update
XkbKeyboardLayoutEngine::xkb_state_ with it.
Based on the original work of Michael Forney <forney@google.com>, in [1].
[1] https://codereview.chromium.org/1841083003/
BUG=578890
Review-Url: https://codereview.chromium.org/2639053002
Cr-Commit-Position: refs/heads/master@{#446529}
17 files changed
