Merge branch 'ar/submodule-gitdir-tweak'

Merge branch 'ar/submodule-gitdir-tweak'

Avoid local submodule repository directory paths overlapping with
each other by encoding submodule names before using them as path
components.

* ar/submodule-gitdir-tweak:
  submodule: detect conflicts with existing gitdir configs
  submodule: hash the submodule name for the gitdir path
  submodule: fix case-folding gitdir filesystem collisions
  submodule--helper: fix filesystem collisions by encoding gitdir paths
  builtin/credential-store: move is_rfc3986_unreserved to url.[ch]
  submodule--helper: add gitdir migration command
  submodule: allow runtime enabling extensions.submodulePathConfig
  submodule: introduce extensions.submodulePathConfig
  builtin/submodule--helper: add gitdir command
  submodule: always validate gitdirs inside submodule_name_to_gitdir
  submodule--helper: use submodule_name_to_gitdir in add_submodule