An attempt at fixing #12168 by only returning the cached data at the child path rather than at the parent

[mortenbekditlevsen]

Discussion

This attempts to fix the issue reported here:

https://github.com/firebase/firebase-ios-sdk/issues/12168

Testing

I will be adding tests to this PR.

API Changes

[mortenbekditlevsen]

I forgot how to run tests when using SPM, so I haven't had any luck with the testing yet.

[paulb777]

Thanks @mortenbekditlevsen! It looks like the tests pass on CI other than needing clang-format.

@maneesht Would you take a look?

[paulb777]

cc: @aashishpatil-g