API graphs calls PromiseFlow::storeStep to propagate promises, which means it missed a store steps added elsewhere in the old promise library model.
We want API graphs to rely on type-tracking steps in general, like in Ruby, but for now just fixing the bug.
With the old test runner we cannot have `VerifyAssertions.qlref`s for each individual test that reference a shared `VerifyAssertions.ql` in the parent directory, since it doesn't like nested tests.
Instead, we have to turn `VerifyAssertions.ql` into `VerifyAssertions.qll`, and each `VerifyAsssertions.qlref` into a `VerifyAssertions.ql` that imports it.
But then that doesn't work with our old directory structure, since the import path would have to contain the invalid identifier `library-tests`. As a workaround, I have moved the API graph tests into a directory without dashes in its path.
