FR: git meta open-all $commitish

I sometimes want to inspect all changes in a particular commit, and it would be useful to have a command that automatically opens all the changes in that commit.

Demo as an alias:
```
git config --global alias.open-all '!git diff-tree -r --name-only -z "$1"^ "$1" | xargs -0 git meta open #'
```
(Bonus points for being able to somehow close any of these "auto-opened" submodules that I didn't have open already.)