Avoid lambda code to cache computer snapshot

The lambda will automatically retain a reference for use within
the code block. In addition, snapshotComputer() also creates a
new object for the snapshot everytime. If the lambda is called
multiple times and some places keep them for a long time, the
snapshot object becomes huge. It causes OOM in the system_server
process and leads to platform reset.
To avoid the problem, use Supplier instead and then gain snapshot
the supplier.

Bug: 381996338
Flag: EXEMPT bugfix
Test: atest FrameworksMockingServicesTests:com.android.server.pm
Change-Id: I57422392167012905243db0856b6eb5648b56489