Add support for cc_library_headers to replace llndk_headers

Set llndk.llndk_headers: true to allow a cc_library_headers
module to be used by a cc_library module with llndk.symbol_file set.

Bug: 170784825
Test: TestLlndkHeaders
Change-Id: Ib65a4b70717dc9a54ae30f2991485bb1bb9b8409