Create action to append additional file_contexts entries. This mirrors the Soong action: https://cs.android.com/android/platform/superproject/+/master:build/soong/apex/builder.go;l=275-284;drc=20b623da8944150be0b7a0a294f7e3246385a3c6 Bug: 236679278 Test: bazel analysis test Change-Id: Ifbf12cb39cee2aca730c60406b851bbee24236bc