Merge branch 'gc/submodule-update-part1'

Merge branch 'gc/submodule-update-part1'

Rewrite of "git submodule update" in C (early part).

* gc/submodule-update-part1:
  submodule--helper update-clone: check for --filter and --init
  submodule update: add tests for --filter
  submodule--helper: remove ensure-core-worktree
  submodule--helper update-clone: learn --init
  submodule--helper: allow setting superprefix for init_submodule()
  submodule--helper: refactor get_submodule_displaypath()
  submodule--helper run-update-procedure: learn --remote
  submodule--helper: don't use bitfield indirection for parse_options()
  submodule--helper: get remote names from any repository
  submodule--helper run-update-procedure: remove --suboid
  submodule--helper: reorganize code for sh to C conversion
  submodule--helper: remove update-module-mode
  submodule tests: test for init and update failure output