Respect resource visibility

[drewhamilton]

An Android resource in a library module can be

• explicitly declared public,
• public by default if the module uses no <public> tags, or
• private by default if the module uses at least one <public> tag but not for the given resource.

It would be great if this Gradle plugin would apply the same visibility to the generated functions: public visibility for functions resolving public resources, and internal visibility for functions resolving private resources.