LayoutLib: Annotate the custom delegate methods.

Every method implementing a delegate needed by the
layoutlib_create bytecode modification must now be
annotated with LayoutlibDelegate.

The methods in the original source code that are delegated
are already automatically annotated. Now with the implementations
being annotated we can do bi-directional tests and find not
only missing implementations but also dead obsolete code.

This will be useful when backporting to earlier versions of
Android, or when native (non public) method disappear. In fact,
the new test detected one such method in Shader.

Change-Id: I491708b68ac2736ca5669aa86cd5e930a00f9db3