Introduce inject_bssl_hash library property.

external/boringssl needs to run a tool on a shared library, but
cc_genrules currently don't support shared libraries as inputs
or outputs.  Use a property to trigger the desired behavior for
now.

Bug: 137267623
Test: m libcrypto
Change-Id: I75b4a761f8a4f2c65a99453d2781d6d0f93106ef