[iOS] Fixing avatar size issue in Consistency Web sign-in

In the consistency account chooser view, the image is to be fetched
at 30x30 size (IdentityAvatarSize::TableViewIcon).
The identity view style needs to be set before setting the avatar
image.

Fixed: 1246520
Change-Id: I2f95443b1f8194113f2ea62444575c0691ec5116
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3141713


Auto-Submit: Jérôme <jlebel@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/main@{#918701}