Add double_loadable property and checks for it

double_loadable is a property that tells whether a module is capable or
being loaded with other instance (possibly an older version) of the same
module in the same process. Currently, a shared library that is a member
of VNDK can be double loaded in a vendor process if the library is also
a dependency of an LLNDK library. Such libraries now must be explicitly
marked as `double_loadable: true` by the owner, or the dependency from
the LLNDK lib should be cut if the lib is not designed to be double
loaded.

Bug: 77155589
Test: m -j
Change-Id: I3b839f860cbdc01f43b59872cd7bb84ac4a7d73e