[iOS] Add OWNERS file for ios/components/ui_util

Use the same OWNERS as ios/chrome/browser/ui/util, since that's where
the code in this directory came from.

Change-Id: I817e7d77df70efcc2ae9e2cc92b05a091736a2a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2133163Reviewed-by: Kurt Horimoto <kkhorimoto@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Livvie Lin <livvielin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756107}

ios/components/ui_util/OWNERS

+kkhorimoto@chromium.org
+marq@chromium.org
+
+# TEAM: ios-directory-owners@chromium.org
+# OS: iOS