completion: hide dotfiles for selected path completion

The completion helper for index paths uses git ls-files rather than shell filename completion. As a result, leading-dot paths such as a tracked .gitignore were offered even when the user had not started the path with ..

Hide leading-dot path components for git rm, git mv, and git ls-files when completing an empty path component. Explicit dot completion is still preserved, so git rm . can still complete .gitignore.

This removes the existing TODO expectations in t/t9902-completion.sh and adds coverage for explicit dot completion.

Validation:

* git diff --check -- contrib/completion/git-completion.bash t/t9902-completion.sh
* bash -n contrib/completion/git-completion.bash
* ./t9902-completion.sh

Zakariyah Ali (2):
completion: hide dotfiles for selected path completion
completion: hide dotfiles by default for path completion

 contrib/completion/git-completion.bash | 53 +++++++++++++++-----------
 t/t9902-completion.sh                  | 19 ++++-----
 2 files changed, 40 insertions(+), 32 deletions(-)

base-commit: 9b7fa37559a1b95ee32e32858b0d038b4cf583e5
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-2311%2Falibaba0010%2Fcompletion-hide-dotfiles-v3
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-2311/alibaba0010/completion-hide-dotfiles-v3
Pull-Request: https://github.com/git/git/pull/2311

Range-diff vs v2:

 1:  056e239e06 = 1:  056e239e06 completion: hide dotfiles for selected path completion
 -:  ---------- > 2:  7482ee4645 completion: hide dotfiles by default for path completion

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