Reland "git-cl: Refactor CMDUploadChange"

This is a reland of 9f29465e

Original change's description:
> git-cl: Refactor CMDUploadChange
>
> Changes:
> - Add _GetDescriptionForUpload and _GetTitleForUpload.
> - Add ensure_change_id to ChangeDescription, that ensures the
>   description has a particular Change-Id.
> - If more than a Change-Id was entered on new issue upload, remove
>   all, and add a new one.
>
> Change-Id: I0eae474eb07ea3036973b18571f72a80da425b21
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2101811
> Reviewed-by: Josip Sokcevic <sokcevic@google.com>
> Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>

Change-Id: Ib2c0ad61b169f6b0c3141674591b0d3fa42bc664
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2103532
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>