feat(gazelle): use relative paths for resolved imports

[adzenith]

Modify the Gazelle plugin so that when it adds a dep because of a resolve directive it makes it a relative import if possible.

The first commit adds a test for the existing behavior, where inside of //package2 the dependency //package2:resolved_package is added. The second commit updates the test and the behavior so inside of //package2 we add :resolved_package instead.

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[adzenith]

Thanks!