Respect package boundaries in bp2build conversion of go modules

bp2build's codegen context does not implement
BazelPathConversionContext. To reuse the utility function
transformPackagePaths, update its signature

(Also make deps of go_library unique to make the conversion resilient)

Test: go test ./bp2build
Change-Id: I126b1057d2b26bc6c7d3be2780f1b62d28323cf0
diff --git a/android/bazel_paths_test.go b/android/bazel_paths_test.go
index 450bf76..60c0a14 100644
--- a/android/bazel_paths_test.go
+++ b/android/bazel_paths_test.go
@@ -175,7 +175,7 @@
 		"./z/b.c": "z/b.c",
 	}
 	for in, out := range pairs {
-		actual := transformSubpackagePath(ctx, bazel.Label{Label: in}).Label
+		actual := transformSubpackagePath(ctx.Config(), ctx.ModuleDir(), bazel.Label{Label: in}).Label
 		if actual != out {
 			t.Errorf("expected:\n%v\nactual:\n%v", out, actual)
 		}