Add ability for make_injection to invalidate itself when Android.bp
files change.

This is a lightweight solution to allow make_injection to invalidate
itself when Android.bp files change their content, so that it can build
the HEAD version of the module requested.

Bug: 210399979
Test: Modify Android.bp file, b test //build/bazel/tests/apex:build.bazel.examples.apex.minimal_content_diff_test (test fails as expected, since the repo rule is invalidated), revert it, and run b test again (test passes as expected)
Change-Id: I0334e5438529df62c7da0c7ff0c7a0db903d214e