Rename traits and mojo directory in //ui/display/mojo

This change renames the folder name, mojo, to mojom and
*_struct_traits.* to *_mojom_traits.* in
//ui/display/mojo.

*_struct_traits.* => *_mojom_traits.*
//ui/display/mojo => //ui/display/mojom
//ui/display/mojo:interfaces => //ui/display/mojom:mojom

Bug: 806965
Change-Id: I445dbab1ca69bbc9fa151ea20369c16bc2763072
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1691963
Commit-Queue: Julie Jeongeun Kim(OoO til July 21) <jkim@igalia.com>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#677886}