image: Fix dangling image detection with graphdrivers

[vvoland]

• fixes: docker image ls -f dangling=true shows no images unless -a is also specified #6699

Fix `docker image ls` dangling image handling

image: Fix dangling image detection with graphdrivers

The isDangling function was incorrectly identifying images as dangling
when they had no RepoTags but had valid RepoDigests.

This can occur when the graphdrivers are used instead of the containerd
image store.

An image should only be considered dangling if it has no RepoTags,
regardless of whether it has RepoDigests.

image/tree: Extract untagged image name to const

image/tree: Fix width calculation for untagged images

When calculating column widths for the tree view, untagged images
weren't being properly accounted for in the width calculation.

This caused layout issues when there were tagged images were shorter
than the <untagged> string.

image/tree: Remove --all flag check for untagged images in non-expanded view

This reverts part of the logic introduced in 207bf52 which
incorrectly gated untagged images behind the --all flag in non-expanded
view.

The original fix was addressing the wrong layer of the problem.

The actual issue was that dangling images were being incorrectly passed
to the tree code in the first place.

This was properly fixed in 67f5e34 which corrected the dangling image
detection logic to properly filter them out before reaching the tree
display code.

Now that dangling images are correctly filtered upstream, untagged
images that reach the tree view should be displayed regardless of the
--all flag setting.

image/tree: Add golden test

[codecov-commenter]

Codecov Report

❌ Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cli/command/image/list.go	0.00%	1 Missing ⚠️
cli/command/image/tree.go	83.33%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[thaJeztah]

LGTM, thank you!