Move c/b/ui/ash keyboard code to subdir

Code cleanup only, no functional changes.

Bug: 843332
Change-Id: I17686724cf4d76c601633a22c6b3c2eeab2458bb
Reviewed-on: https://chromium-review.googlesource.com/c/1364060
Commit-Queue: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Darren Shen <shend@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614227}
41 files changed