gn2bp: propagate static libs up the tree

Soong explicitly requires to list all static libraries, including static
libraries that are linked by a dependency.

What is interesting is that this change seemed to have introduced new
targets?! Will have to check if that's correct, but at first glance it
seems to make sense.

Test: //components/cronet/android:cronet
Change-Id: I0e6e9a760dd0a4ebc5ce50f5dabc02458ff488a8