Allow the system AssetManager to be reinitialized for testing

ResourcesPerfWorkloads replays record resources calls for 1P and 3P
apps. The recordings use private resource ids. Since private
resources ids can change between builds, the replay must have the
ability to use a stable version of framework resources with the
correct resource ids.

Bug: 136085555
Test: atest ResourcesPerfWorkloads
Change-Id: I46297e355ed6347ce8063e7f1c26708f28faacc8