Use a ReferenceQueue to prune weak references

Currently ResourcesManager iterates over all of its weak references to
Resources objects and calls Reference#get to determine if the object
has been garbage collected. This method of pruning WeakReferences
causes reference locks to be acquired in the native layer and causes
lock contention when "references are being processed" by the garbage
collector.

This change uses a ReferenceQueue to determine if a reference has been
garbage collected which should improve performance of
ResourcesManager#getResources when the system is under memory pressure.

By only removing garbage collected references when creating new
Resources objects, the lists grow larger and are periodically pruned
rather than attempting to prune entries from the list every getResources
invocation.

Bug: 157575833
Test: used debugger to observe pruning happening correctly
hange-Id: I3277e80edfa441d24de165e738d33c4fac6b4121
Change-Id: I3277e80edfa441d24de165e738d33c4fac6b4121