Add tetsui@ to ARC IME OWNERS

BUG=None
TEST=None

Change-Id: Ia27fc34352eee14d97f56e7af6a01fdd9274ae32
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1828777Reviewed-by: Kazuhiro Inaba <kinaba@chromium.org>
Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#701014}

components/arc/ime/OWNERS

 kinaba@chromium.org
+tetsui@chromium.org
 yhanada@chromium.org
 
 # COMPONENT: UI>Input>Text>IME