Diffs: Model files newly returned from gitaly

Gitaly's https://gitlab.com/gitlab-org/gitaly/-/merge_requests/5680
allows for returning information about all files in
a diff, not just those that do not exceed file limitations.
Add handling for this in Gitlab to request the metadata for diffs that
exceed set limits and ensure diff collections process
the added metadata as diffs to be stored.

lib/gitlab/git/diff#Diff: Add overflow attr

gitlab/git/diff.rb#Diff: make `collect_patch_overage` a predicate method

gitlab/git/diff.rb#Diff: prune guard on overflow

gitlab/git/diff.rb#Diff: fixup typo

gitlab/git/diff_collection.rb#DiffCollection: force consideration of feature flag

gitlab/git/diff: Review formatting suggestions

gitlab/git/diff_collection: make collect_all_paths a class method

lib/gitlab/git/diff.rb: Reduce one off method useage

spec/lib/gitlab/git/diff_spec.rb: Correct constructor signature

spec/lib/gitlab/git/diff_spec.rb: rubocop

lib/gitlab/git/diff.rb: rm dangling ref

spec/lib/gitlab/git/diff_spec.rb: simulate patch pruned by gitaly