mixed build targets need transitive tidy files

Previously in mixed builds, only the tidy files for the boundary module
were built, whereas all of its transitive dependencies' tidy files were
not being built. Instead we should export the list of transitive tidy
files for a module so that we can run clang-tidy for the boundary module
as well as its dependencies.

Bug: 195029134
Test: WITH_TIDY=1 DISABLE_ARTIFACT_PATH_REQUIREMENTS=true mss tidy-packages-modules-NeuralNetworks --bazel-mode-dev
Change-Id: I463646d2ae1fc4aa075a54c264e1c34571c3fd5c