java_sdk_library: Propagate shared_library to snapshot

Passes the shared_library property through to the snapshot. It does not
optimize away the default value in order to make it easier to invert
the default value in future. The current default value was only chosen
for convenience because most existing usages were already treated as
shared libraries. It would be safer if modules had to opt in to be used
as shared libraries.

Bug: 155164730
Test: m nothing
Change-Id: I33c7323f2389b44ed49cebe517ae2cce349117f1