ab/submodule-helper-prep-only (was: What's cooking in git.git (Nov 2022, #01; Thu, 3))

> * ab/submodule-helper-prep-only (2022-11-02) 8 commits
>  - submodule--helper: use OPT_SUBCOMMAND() API
>  - submodule--helper: drop "update --prefix <pfx>" for "-C <pfx> update"
>  - submodule--helper: remove --prefix from "absorbgitdirs"
>  - submodule API & "absorbgitdirs": remove "----recursive" option
>  - submodule.c: refactor recursive block out of absorb function
>  - submodule tests: test for a "foreach" blind-spot
>  - submodule tests: add tests for top-level flag output
>  - submodule--helper: move "config" to a test-tool
>
>  Preparation to remove git-submodule.sh and replace it with a builtin.
>
>  Waiting for review?
>  source: <cover-0.8-00000000000-20221102T074148Z-avarab@gmail.com>