More options to @DefaultQualifier: member type, modifiers

Please add more options for finer-grained control over which annotations are 
applied to which program elements by default. 

Here are two requested features:
 * target annotations at fields without targeting methods or the enclosing class
 * target based on a combination of modifiers (visibility, static or not, final or not) 
This would be especially useful for classes that hold untrusted data parsed 
from JSON or XML.

This is what the extended @DefaultQualifier API could look like when used in a 
package-info.java file:

@DefaultQualifiers({
  @DefaultQualifier(value = Nullable.class, targets = {
    @Location({ PUBLIC, NON_FINAL, FIELDS }), 
    @Location({ VOLATILE, FIELDS })
  }),
  @DefaultQualifier(value=NonNull.class, targets = {
    @Location({ PUBLIC, STATIC, FINAL, FIELDS })
  })
})
package some.component;

import static checkers.quals.DefaultLocation.*;
import checkers.nullness.quals.NonNull;
import checkers.nullness.quals.Nullable;
import checkers.quals.DefaultQualifier;
import checkers.quals.DefaultQualifiers;
import checkers.quals.Location;

That package-info.java file would override the default annotations to be set 
like this:

class ContrivedExamplePerson {
  public static final String JOB_1 = "koodari"; // @NonNull
  static volatile Boolean isValidationComplete; // @Nullable

  public final String recordType = "minimum";   // not overridden
  public String name;                           // @Nullable
  public String occupation;                     // @Nullable
}

Original issue reported on code.google.com by timo.kin...@gmail.com on 9 Feb 2013 at 1:42

Start with the @DefaultQualifier and @DefaultQualifiers API as used in package-info.java, and trace how annotation targets are currently interpreted. Compare that behavior with the requested field-only and combined modifier locations; done means the shown Nullable and NonNull defaults can express the requested outcomes.