Unify coding style of the SPI interfaces

The JLS says:

For compatibility with older versions of the Java platform, it is permitted but discouraged, as a matter of style, to redundantly specify the abstract modifier for methods declared in interfaces.

It is permitted, but strongly discouraged as a matter of style, to redundantly specify the public modifier for interface methods.

The vast majority of CDI API interfaces specifies the public modifier while leaving out the abstract modifier, however, there are exceptions:

public interface Context {
...
    boolean isActive();
}

public interface BeanAttributes<T> {
    public abstract Set<Type> getTypes();
    public abstract Set<Annotation> getQualifiers();
...