bp2build: Add support for export_.*headers props

Soong supports export_.*_headers properties, the libraries contained in
this list must also be within a shared/static/whole_static/header libs
property. For bp2build, we eliminate this duplication. The libraries
not listed in an export_.*_headers property will migrate to an attribute
prepended with implementation_, those in export_.*_headers will not have
a prefix.

Test: build/bazel/ci/bp2build.sh
Test: build/bazel/ci/mixed_libc.sh
Bug: 198241472
Change-Id: I3eb84c983ec5d241c8a568e411dfd5619d3184a7