Use Soong modules for the NDK's extra STL libraries

 * The extra STL libs are:

       libc++abi.a [needed for ndk_libc++_static]
       libandroid_support.a [always needed in NDK r16]
       libunwind.a [needed for ARM32]

 * The existing STL-dependency logic in linkShared only applies to shared
   libraries. By moving it to STL deps, the extra STL libs are linked into
   both shared libraries and executables.

 * Remove the ndk_prebuilt_library/ndkPrebuiltLibraryFactory module type,
   which is unused now.

 * Reuse the ndk_prebuilt_static_stl module type to describe the extra
   static libraries that are linked with both the static and shared libc++
   STLs.

Bug: b/73133405
Test: manual
Change-Id: I3f73e4f882d39e6efa470073bb4fc8c42dff8253