Merge branch 'ps/ref-consistency-checks'

Merge branch 'ps/ref-consistency-checks'

Update code paths that check data integrity around refs subsystem.
cf. <CAOLa=ZShPP3BPXa=YnC-vuX4zF=pUTFdUidZwOdna8bfVTNM9w@mail.gmail.com>

* ps/ref-consistency-checks:
  builtin/fsck: drop `fsck_head_link()`
  builtin/fsck: move generic HEAD check into `refs_fsck()`
  builtin/fsck: move generic object ID checks into `refs_fsck()`
  refs/reftable: introduce generic checks for refs
  refs/reftable: fix consistency checks with worktrees
  refs/reftable: extract function to retrieve backend for worktree
  refs/reftable: adapt includes to become consistent
  refs/files: introduce function to perform normal ref checks
  refs/files: extract generic symref target checks
  fsck: drop unused fields from `struct fsck_ref_report`
  refs/files: perform consistency checks for root refs
  refs/files: improve error handling when verifying symrefs
  refs/files: extract function to check single ref
  refs/files: remove useless indirection
  refs/files: remove `refs_check_dir` parameter
  refs/files: move fsck functions into global scope
  refs/files: simplify iterating through root refs