Most modules will be providing their implementations via APEX and so do
not need to create an implementation shared library as part of this.
Adds an api_only property which will:
* Prevent the creation of the implementation library.
* Prevent the creation of the .xml file needed at runtime to make
the shared library available.
* Prevent the library being added to the list of java sdk libraries
used by make to handle installation.
Bug: 145998881
Test: m checkbuild
Change-Id: Ida5e46a81aa5b0a041882d90d5f362ec79fdddb2