[bazel.build] /rules/lib/builtins/Args fails to document requirements for using expand_directories=True

### Page link:

https://bazel.build/rules/lib/builtins/Args (and older versions)

### Problem description (include actual vs expected text, if applicable):

I wasted about an hour yesterday trying to debug why my starlark wasn't working (in a fork of bazel 7.5.0) before I stumbled onto https://github.com/bazelbuild/bazel/issues/11811. From that issue I was able to understand that the tree artifact I was using needed to also be an input to my action, despite only needing the filenames from it - or else I'd get an empty list. Apparently this gives a useful error in newer bazel versions, but I am not blessed enough to be using the new version, and documenting this would be useful either way.

### Where do you see this issue? (include link to specific section of the page, if applicable)

https://bazel.build/rules/lib/builtins/Args.html#add_all
https://bazel.build/rules/lib/builtins/Args.html#add_joined

also probably should be mentioned on https://bazel.build/rules/lib/builtins/DirectoryExpander

And old version of all of the above as well.

### Any other information you'd like to share?

_No response_

Start with the linked Args add_all and add_joined sections and the DirectoryExpander page, then compare the corresponding older-version pages. Trace the reported expand_directories=True behavior and the requirement involving tree artifact inputs. Done means the requirement is clearly documented in each relevant current and older-version location.

Written by the indexing model from the issue text.