Remove the dependency on Mockito to create QS actions fakes (1/2)

This CL refactors FooterActionsViewModel so that it can be created
easily with fake values in the Gallery app and screenshot tests. That
way, we don't need to depend on Mockito to create fake dependencies of
the ViewModel, which is necessary for deviceless RNG tests (and better
architecture) and Compose @Previews.

This is a pure refactoring that doesn't change any logic in the code.

Bug: 304719047
Test: atest FooterActionsScreenshotTest
Change-Id: If5841b32b84ff3f7ac8d9d1d42449da481dc9b55