Add a directive for ignoring imports

[mrkkrp]

Based on #34.

The motivation here is that sometimes certain internal crates re-export modules which looks to the plugin as if we are depending on those modules directly. It is desirable to have a mechanism for avoiding these false positives.

[mdeville]

@mrkkrp Hey,
Thanks a lot for this new directive :)
However I realized that it seems to apply the behavior automatically to sub-packages too.

If I add it to a BUILD.bazel file, then all BUILD.bazel files in sub-directories have their dependency removed.
I think it should only do it for the current file.

What do you think ?

[mrkkrp]

Hey @mdeville, good catch! I have adjusted the PR to make the new directive local to the BUILD file where it is used. I have also adjusted the test accordingly.

[Calsign]

FWIW I normally expect directives to apply recursively to subdirectories. From the gazelle docs:

Directives apply in the directory where they are set and in subdirectories.

But there isn't an obvious way to override or undo this directive in a subpackage, so I suppose this OK.

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gazelle_rust also has the import macro, i.e.:

#[gazelle::ignore]
use foo::bar;

but I can see a directive being useful as well.

[mrkkrp]

@Calsign I've rebased the PR.