[Fuchsia] Add ddorwin to OWNERS

Also alphabetize the list.

Change-Id: I01fef1a4b0d0681b108c7b69fa5ce2c14d7dfd26
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2143032Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#757813}

build/fuchsia/OWNERS

-kmarshall@chromium.org
+ddorwin@chromium.org
 fdegans@chromium.org
+kmarshall@chromium.org
 sergeyu@chromium.org
 wez@chromium.org