Store hard refences in a static context and pass through only weak

references during the Content Capture Sharing.

Motivation: if the remote app is killed, we don't want a possibility of
system server holding a stroing reference (through a reference chain)
to large objects in that app. Therefore what's send in the binder has to
be a weak reference. And we will store a hard reference to those objects
in the client app's static context.

Storing hard references to objects in system_servier is less critical, because that is not going to be killed.

Bug: 148265162
Test: covered by CTS tests
Change-Id: Ie561aab6019d191cf8659fb350e045089e7781ed