[iOS] Move SwipeView to its own file

This is a preliminary step to start using it for the "Switch to this
tab" feature.

Bug: 893121
Change-Id: I58f9095b689dbd0a59fffcb20bca7924dd239d7f
Reviewed-on: https://chromium-review.googlesource.com/c/1319675
Reviewed-by: Justin Cohen <justincohen@chromium.org>
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605994}
4 files changed