Improve immune spaces logic

We now properly include the largest continuous region with the most
image bytes. Oat bytes are considered as part of the region but are
not counted when comparing. This can result in more image bytes in
cases where large oat files were previously included for the immune
region.

Also added handling for adjacent oat files:
[image][image][oat][oat][space] will now properly be a single region.

Bug: 27136196

(cherry picked from commit 17b8bce0)

Change-Id: Ic69489fef1ba72f735ee613d5416eeadc703c06e