Follow-up from "Update tree and blob resolvers to accept ref_type"
Address some non-blocking comments from: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/122144 - https://gitlab.com/gitlab-org/gitlab/-/merge_requests/122144#note_1429958536: We should refactor common logic in `BlobPresenter` and `TreeEntryPresenter`: - https://gitlab.com/gitlab-org/gitlab/-/merge_requests/122144#note_1429958547: Consider renaming the `.ref_type` method to something more meaningful - https://gitlab.com/gitlab-org/gitlab/-/merge_requests/122144#note_1429958527: Namespace `Types::RefTypeEnum` - https://gitlab.com/gitlab-org/gitlab/-/merge_requests/122144#note_1429958556: Namespace `ExtractsRef`
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