add clang-tidy files to independent output group

Clang tidy actions should be run as validation actions, but in order to
get them easily from mixed builds in Soong, we should add them to their
own output group.

Test: b build //packages/module/adb:adb_test
Test: m --bazel-mode-dev adb_test
Change-Id: Iac2566f836b8bb00fffcc0cfb12652d6ffb899a4