Add "provide_cpp_shared_libs/uses" props to "apex"

For APEXes to share C++ native libraries, we need a new kind of depedency
between APEXes: "providing" APEXes and "using" APEXes. To reflect this
dependency two new properties are added.

provide_cpp_shared_libs: bool
  this indicates that the current APEX module provides the native C++ shared
  libs to other APEXes.

uses: []string
  this indicates that the current APEX module uses the native C++ shared
  libraries from APEXes listed.

With these two, "using" APEXes can omit shared libraries in its APEX
bundle and use them from the "providing" APEXes.

Note that without corresponding changes in ld.config.txt, this won't
work.(The linker namespaces should be configured so that user APEX can
access provided libs.)

Bug: 136975105
Test: m nothing (this will trigger soong's test)
Change-Id: Iec6f9f67bcbde01145acc383f862ba21c8197536