Use R field directly for shared lib styleable attrs

If a shared library exposes an attribute and a client uses the
attribute in its own styleable, the value of the lib attribute
resource id in the client styleable must be fixed with the correct
package id at runtime. Since the client will not have an
onResourcesLoaded to call, the client should directly reference the
attribute resource field in its styleable.

Bug: 147674078
Test: aapt2_tests
Change-Id: I8e64bb2d3165a7072e2604fe1730b248545978f4