Add the initial implementation of bp2build converter for java_library,

java_library_host, java_binary_host and cc_library_host_shared so
signapk tool can be built with Bazel.

Test: b build //build/bazel/examples/apex/minimal:build.bazel.examples.apex.minimal
Test: jarsigner -verify -verbose build.bazel.examples.apex.minimal.apex
Bug: 209876137
Bug: 196204358
Bug: 210158864
Bug: 210159074
Bug: 210158872
Change-Id: I855884159d25e69d8f9623792c376da820a1eb4c