Implementation of the FooterActions following the MAD (1/3)

This CL provides most of the implementation of the QS FooterActions
following the modern Android architecture. In particular, this CL
includes:
 - repositories in the data layer.
 - an interactor in the domain layer.
 - a view model in the ui layer.

The ViewBinder is added in ag/19674347, given that it comes together
with changes to the existing XML files.

Note that after this CL, the new implementation will still not be used
as it won't be wired yet. This is done in ag/19674347.

The highest value of the tests is in FooterActionsViewModelTest, which
focuses on testing the *state* (view model) of the footer actions using
the *real implementation* of the repositories, interactor and viewModel
all together. To do so, I implemented a FooterActionsUtils class that
allows to *easily* create real implementations of those repositories,
interactor and view model, without requiring the caller to provide any
parameter. I believe that this is even better than introducing new
fakes, and it should hopefully lead us towards using more and more of
the real implementations in our tests, and less and less of fakes/mocks,
making the tests much more useful. Of course, I still had to use fake &
mocks for the classes I'm calling to and for which instantiating the
actual object is too painful. As you can see, there are no test files
for the repositories: given that we already use the real implementations
in the ViewModel tests, they are defacto already tested.

I still added some tests on *interactions* (not *state*) in
FooterActionsInteractorTest. Even though I believe those tests don't
provide much value (they are merely a copy/paste of the implementation),
I preferred keeping the same coverage as the current tests (some of
which are going to be removed in ag/19674347).

Note that the business logic contained in this CL was mostly copy/pasted
from the current implementation, as I wanted to make sure that this is
going to be a pure refactoring that does not change the logic of this
feature. Still, I left some TODOs in the code for potential
improvements.

Bug: 242040009
Test: atest FooterActionsViewModelTest
Test: atest FooterActionsInteractorTest
Change-Id: Ia0bdf9824e098ad6604709f5db87576437b0a904