Merge branch 'ar/submodule-gitdir-tweak' into seen

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

* ar/submodule-gitdir-tweak:
  t7425: add gitdir encoding tests
  t7450: move nested gitdir tests to t7425
  submodule: remove validate_submodule_git_dir()
  submodule: error out if gitdir name is too long
  submodule: encode gitdir paths to avoid conflicts
  strbuf: bring back is_rfc3986_unreserved
  t7425: add basic mixed submodule gitdir path tests
  submodule: add gitdir path config override
  submodule: create new gitdirs under submodules path
  submodule--helper: use submodule_name_to_gitdir in add_submodule

diff --cc Documentation/fetch-options.adoc
Simple merge

diff --cc Documentation/git-submodule.adoc
Simple merge

diff --cc Documentation/gitsubmodules.adoc
Simple merge

diff --cc Makefile
Simple merge

diff --cc builtin/submodule--helper.c
Simple merge

diff --cc meson.build
Simple merge

diff --cc setup.c
Simple merge

diff --cc submodule.c
Simple merge

diff --cc t/meson.build
Simple merge

diff --cc t/t6120-describe.sh
Simple merge

diff --cc t/t9902-completion.sh
Simple merge