Refactor libart_runtime_headers_ndk to a header lib also used by libart
itself.

This renames it and drops `sdk_version: "current"` as well.

Test: art/build/apex/runtests.sh
Test: m art-module-sdk art-module-{host,test}-exports
Bug: 204364566
Change-Id: I62c18fb1406e96865ad60d5022dcc4b60e778cbd
3 files changed