bp2build: support strip properties.

This CL adds support to bp2build for generating all strip-related
properties into a strip dictionary as a parameter in the cc_library
macro.

With the dictionary, it's easy to organize related attributes and
directly expand into a stripped_shared_library's attributes.

Test: //build/bazel/tests/bionic:compare_libc_stripping
Test: TH
Fixes: b/187928597
Change-Id: Ifea68d48fe295e71a43b12876cb168c475a62187